The Tsarista is the Mechanised Archon - A theory (includes Honkai Impact 3rd lore)
God is Dead...But Will It Continue To Be So?
So far up til Fontaine the death of gods has lead to three outcomes:
Their essence becoming corrupting influences and needing to be sealed away (Obarashi, the Thunderbird, Guizhong potentially)
Fading away after the god's soul has been put at peace (Makoto)
Being vored absorbed by the Sovereigns (Deshret, Nahida and Apep, Focalors and Neuvi)
Natlan's chapter is titled "Ode to Resurrection", and with the lack of information that we have about the Pyro Archon, many have speculated that she might be the one resurrecting when the Archon Quest comes around since Focalors Christ died and the next Archon will always be a contrasting character from their predecessor. I mostly agree with this viewpoint but with some extra steps which I will explain in more detail in a future post. But first, let's skip to the Tsarista. If the Pyro Archon will be resurrected, then Tsarista will have to be something beyond. Beyond the natural states of life and death, and artificial extension of what should have died...
Da Bronya
Out of all the Bronya expys that have appeared in Honkai Star Rail, none of them have been based on the original teenaged Bronya Zaychik, the little Russian child assassin whose heart was so full of love that she gave herself brain damage just to stay a few more minutes with her beloved, who gifted her a kick-ass floating mecha that she uses for battle and mobility. I think HoYo is saving that Bronya as the base for the Tsaritsa. When Childe says "Her Royal Highness the Tsaritsa is actually a gentle soul. Too gentle, in fact, and that's why she had to harden herself,"Β he might mean it both metaphorically and literally.
Perhaps during the Cataclysm she returned alive but heavily injured to the point where she needed mechanical prosthetics, thus tying back that hanging plot thread about the the Abyss building a "mechanised god" to oppose Celestia all the way back in We Will Be Reunited.
I think it would also explain why there are two mechanics in the Fatui Harbingers - Dottore is the GP doctor with general wide-reaching knowledge who is also doing his own research to improve Fatui military capabilities while Sandrone is the specialist who can do things Dottore cannot. It would be funny if Dottore's title is supposed to reflect how he is Teyvat's highest ranking quack doctor, but mostly this would contextualise his description of the deification of Scaramouche as an experiment - its like a medical researcher trying to see the effects of new drugs on mice before it is approved for human consumption. His lack of care about how the Shouki no Kami's existence would have threatened the Tsarista plan's can then be justified as proving that it is possible to build fully mechanical gods are on the same level as Archons by human hand, and the Fatui's plans to oppose Celestia would be a step removed from delusion and closer to reality.
On the other hand, with what is implied after the events of the various Fontaine World Quests, my current guess is that Sandrone are working on the backup solution in the event the Tsarista's actual body is unable to continue sustaining her consciousness and needs to be transferred, or replicating her mind. If HoYo wants to go that direction we might get a Prometheus expy. And what was Prometheus' role in HI3? Became the "Honkai god" and restrained the Honkai so that predictable enemies are sent for humanity to defeat, and in turn she was viewed as the greatest force of evil for the longest time until the last few chapters of Part 1. In Genshin, there has been a similar theme of repeating cycles of eras and it may be likely that something similar has been done so that humanity will eventually learn how to be its king of kings and break the shackles of destiny that Celestia wrote into the stars.
Perhaps I'm relying too much on HI3 for this theory, but in the end I think a mechanised god is a cool concept no matter how one looks at it and just want to have a preliminary talk about the possibility of that happening.