千年万岁，椒花颂声

Generally speaking, I'd bet money we start in late winter/early spring 1885. (Season 3 ended in September(ish) of 1884.) All three prior seasons have started at that time of year, and Sonja is on record saying that the season will take place in 1885 and a bit of 1886, so I'm guessing there's no 1884 in Season 4 at all.

Two bits that don't obvious fit elsewhere below. The Statue of Liberty ticker tape parade has been widely leaked. According to this flyer it happens in show-land in Oct 1885, so I'd guess it's near the end of the season? And there's some orientalism afoot. Doubtful that they'll engage with it much beyond aesthetics, but there are opium dens and the rampant abuse of Chinese immigrants during railroad construction to engage with should they choose to.

Now for the characters:

Bertha

We get one shot of Bertha entering 61st St and preparing to greet someone with seeming warmth. This looks like a traveling cloak to me, though lots of speculation that it reads like maternity wear. I'd say that it's her returning from England where she's been for Gladys's birth, but then who is she greeting so warmly?

Then we get a series of clips with this dress

Agnes says, "Please tell me who did you buy to get them over to your side?" and Bertha says "Life's meaning isn't where we came from, it's where we're going." Definitely in the same scene but not necessarily in that order, though if I had to guess I'd say it would be and it relates to Agnes's new VP position preserving the city's history.

Christine says she gets to go "head-to-head" with Bertha which implies this could be an actual plotline.

Possible casting notices related to that plot:

Mrs. Knapp Curtis, the trailblazing editor of the popular periodical The Ladies’ Home Journal -> maybe part of one of their campaigns to build/preserve whatever it is they're fighting about

Lee Klein, an artist who sells his first painting at an unforgettable Society event, and an apprentice to the famed artist William Merritt Chase -> "unforgettable society event" feels quite Bertha

Nurse Virginia Saville, a kind nurse who works at the Neighborhood Settlement House in the Lower East Side -> more doubtful, but perhaps related to whatever area will be torn down/preserved?

Same dress as before, but Bertha's looking back over her shoulder now with some real foreboding. George returning to 61st St? Who knows.

In terms of plot beats I'd bet: ep 1, in England with Gladys; ep 2-4, in NYC estranged from George, striving and fighting with Agnes; then some version of reconciliation/need a united front against enemies to round things out.

George

We've got two clips of George from the leaked upfronts BTS. In neither does he appear to be doing particularly well. "Things have changed, keep up!" could be being said to just about anyone. Worth noting that he's saying it from his home office, so he does pop up there at least at some point. Perhaps he's back at home, or maybe he just works from there sometimes. He also is drinking, and seems a little unkempt and tired also in bts stills, so odds are up on an addiction storyline.

Possible casting notices related to this:

Grover Cleveland, the 22nd President of the United States, who comes to New York to curry favor with the elite class.

Daniel Manning, a seasoned politician and Secretary of the Treasury under President Grover Cleveland.

(Casting calls for presidential entourage, featured dinner guests and presidential dinner guests)

John D. Rockefeller, the famed businessman and oil tycoon. A thin, self-made man of humble origins, now one of the richest and most powerful in the world. A devout Baptist and philanthropist, he does not always see eye to eye with his fellow robber barons

Dr. Reginald Harris, William Kirkland’s mentor, who visits New York to fundraise for the Freedman’s Hospital in Washington, DC, and makes a surprising connection

Ok, so (at least) two sets of plot lines hinted at here. Cleveland is in town and appears to come well before the ticker tape parade that's leaked to try to "curry favor". There's going to be some kind of dinner while he's in town and some political plot lines. It's worth noting that Cleveland famously screwed over men like George by, you know, actually applying a regulatory framework to the railroad industry which was a bit of a financial wild west at the time. No idea if they'll get into this, but could be fodder for Morgan's quote that "things aren't getting any better for George" in addition to the addiction possibility.

Second plot relates to Rockefeller. I've speculated that post-shooting George will want to make his life "meaningful" and rich people often do that by giving money/naming things after themselves/getting legacy. Rockefeller certainly did, so maybe he helps George see there's a better way to robber baron?

Biggest speculatory swing is that the "surprising connection" for Dr. Harris is George. If they really do an addiction storyline, maybe he helps George recover? If they don't, maybe the doctor's fundraising solution is George? Not a crazy leap given that he's Kirkland's mentor. Could easily be a "I know a handy robber baron who owes me one, want me to send him a note" kind of moment. (If George does get sober with help of a Kirkland-adjacent Black man, I will take my royalties in the form of bts Carrie Coon content pls, HBO? Jk...but also?)

Larry and Marian (and Jack)

First we get a pair of scenes with Marian in this blue dress. She and Larry are out dancing and then she looks shocked. No engagement ring on and she's not in a tiara so they're definitely not married/engaged yet.

But we do have Bridget seemingly overseeing them put out an awful lot of white flowers. Could be for Oscar's wedding celebration? Though I kind of think Oscar/Enid will tie the knot off-screen and already be married by the time the season starts. If so, maybe this is to celebrate a re-engagement?

Jack and Larry are still hanging out (possibly working together?) though Larry also has a new job as the producer of Pirates of Penzance. He also, at some point, runs through the ticker tape parade for the Statue of Liberty looking concerned.

Possibly cast related:

Nurse Virginia Saville, a kind nurse who works at the Neighborhood Settlement House in the Lower East Side -> lots of speculation that Marian will want to get into nursing post-saving George, so perhaps this is related to that

Porter, a young gentleman of Society with an Ivy League education and money to invest in exciting new ventures -> plausible that Jack's looking for investors (with or without Larry) and bumps into him

Fiona Summers: cousin to the prominent Astors, Fiona is a free-spirited young woman from a good family who is not afraid to explore the limits of convention -> feels like she's most likely to crop up with Larry and Marian?

Peggy and Kirkland

I don't have screenshots, but from the synopsis and leaks so far it seems they are not married yet at the start of the season. I'm guessing they justify the longer engagement because Mrs. Kirkland is continuing to be a pill about everything. There were casting calls for Black elite "event guests" in Troy which strongly seems like it would be for Peggy's wedding. (Troy is Black Newport, which will never not be funny in a very dark way to me.) So I'd guess, a couple of eps of lead-up wedding drama, then a fairytale wedding and then...? No obvious hints so far.

Gladys and Hector

Both are notably absent from any of the footage out so far. I'm guessing this is because the footage of them is all more heavily spoiler-y so they're avoiding including it.

This casting call seems very likely to be for Gladys's baby. (Newport is where they film Devon as well.) If so, perhaps the main scenes they've shot of either of them so far involve Gladys very pregnant (which would spoil how big of a time jump we have) or Gladys with a baby (ditto).

As for plot lines, no hints. If I had to guess, they'd turn up in the states again at some point (maybe towards the end of the season) but who knows. I assume we will never get closure on how George found out Gladys was pregnant (and happy) and why that failed to remove the stick up his ass, but perhaps miracles do happen.

Oscar (and Enid) + Agnes and Ada

Oscar has some fun new facial hair. Agnes is fighting with Bertha. Agnes and Ada are still fighting for dominance at home. Nothing major to report.

There are also a few shots of Bridget in out-of-work clothes, so presumably more of her going out and about (with Jack?) in our future.