Have you considered
France x Austria
Austria x England
Austria x Russia
and much more?
AS A MATTER OF FACT YES I DIDDLY DOODLY HAVE ANON, hear ye as one of the connoisseur of APH Austria we have this knack of multi-shipping our princess for reason that he makes such good material for it backed by the historical precedent, never forget Matthias Corvinus' "Where Mars gives other kingdoms, Venus gives to thee," in regards to the Habsburgs' renowned marriage strategy!
✨ Now buckle up anon ✨
France x Austria : historically the most disastrous and problematic and terrifying nightmare fuel for the rest of the continent. In fact, some 80% of the conflict had been because of these bitches' rivaling houses having beef with each other. Think the popular pretty girl VS the other popular pretty girl type of dynamic but when they're working together it's both the worst thing possible for everyone and each other because both will stab the shit out of one another. I love them.
It's very possible on a more intimate level the two are able to get along for the fact they're very much two sides of the same coin and are simply dressed differently is all. Both would know the worst of each other and their most vulnerable, I feel their intimacy and bed related activities would be wild — smth smth sex is the rawest form of expression to relinquish control and they'd delve into it. Romantic wise I can see the two being the type to go, "Love doesn't suit our rotten souls."
England X Austria : they're quite an interesting one to me! Anon and everyone will notice a pattern here that I go more for a historical basis route and damn it it's because I remember them better than having to go search through canon material sO — anyhow, Anglo-Austrian relation is a real thing as much as it was quite a... Unique situation between the two. There were the Austrian Anglophiles who insists an alliance with them is efficient to oppose the French (it's always the French)
As much as both had the knack of not fulfilling their end of the bargain to each other as promised because of "changing circumstances". Like we saw in that one episode where England upped and left Austria be during the war of the Austrian succession because he just wanted to beat up France, yeah? That example was demonstrated several more times between the two in the course of their supposed alliance. Roderich and Arthur would have this dancing around one another type of thing going on because they strike me as the type to be more calculative before ever getting personally close when both were the huge superpowers in that time period. And given the British and Spanish had already existing beef whilst the Spanish and Austrian Habsburg branch were united as is, you can see the conflict of interest that created the "they'll be good if we need to kick the French but also our Spanish relatives are important but hurm,"
Personally it was that incident during when the Spanish forces were trying to recapture Gibraltar from the English that lends to this complex dynamic because they asked helped from the Austrians for support only for, whatever REASON, they backed the English forces. This was in the 1700s I believe? I'd like to think England may have bedded the pretty Austrian for that LMFAO.
Russia X Austria : Whew. Okay this one has been quite the guilty pleasure for me ngl. Smth about the domineering force that was the Russian empire, the menacing bear that is Vanya and considering the number of fairly decent alliances the Austrian maintained with their Russians (partitions, holy league, etc.) Roddi and Vanya would have an amicable relationship. I'd think Roderich would have had the sense of walking on eggshells around this person for reason he can just tell at first glance to thread carefully or be at the mercy of whatever Russia would choose to impose of him.
Something like a faux compliance from the most dangerous beast for the pretty sweetling, giving Roderich this false sense of control that maintains the apparent "harmony" of the relationship. They're actually so interesting ngl that I'm sure there's a number of pretty good historical references to grow them with!
Honourable mentions that have been lingering in the back of my mind that aren't the big popular ones —
• Turkiye X Austria : COFFEE CULTURE!! also coughs they have the kind of enemies to lovers vibe I dig
• Poland X Austria : wouldn't you know it that not only during the partitions were the Austrians most lenient towards their polish citizens but consider many times, they had been allies too — I believe marriage arrangements between their monarchs were planned as well but unfortunately couldn't come to fruition
• Netherlands X Austria : Okay here we go babes before they were Netherlands they were the low countries and under whose house if not the HRE and then the Habsburgs by way of claim through marriage to the Spanish for inheritance, and if not ship material why did they have good relations including an Austrian monarch marrying into the Dutch to help them fix up governance and they flourished? Also tallest man bagging the prettiest princess who was once married to his rival (Spain) is the single funniest addition to this
• Denmark X Austria : Listen. I haven't seen many touch into this but not only do they share actual pastry influence with each other, during the second Schleswig-Holstein conflict, it was by the Prussians recruiting the Austrians they managed to beat the Danish and I imagined it was the princess straight up stabbing the shit out of Denmark that had the Dane be horny at first sight and well, when you're the winner of the war you'd want to get your spoils, no?
