Randomly got linked this thread, and golly! As an
advocate for a successful Ičko's Peace TL, or rather, a TL that involves the Russians to a lesser degree than OTL, per my
signature, this is quite an interesting scenario.
Part of the reason why I find an Ičko's Peace scenario so interesting is because it enables the fledgling revolutionary republic to decide for itself whom it would side with, which, in a scenario where Russia and France may fight or might work together or anything, sounds like an attractive prospective. Plus, we already have somewhat of an idea what the policies demanded by the peace would look implemented, to a degree, given how Obrenović's Serbia would get them belatedly implemented by the 1830s. And most interesting for me, a lot of the post-1807 institutional changes, especially post-1811, are avoided, which weakens Karađorđe's position and enabled Serbia to actually possibly be a republic, which could have its own quirks.
In contrast here, Serbia is very much stuck in terms of whom it might side with, especially since it's clear in this scenario that Russia and France will inevitably fight. With Austria bolstering up Bosnia, Serbia is definitely going to be on the side of the Russians, and that means the Russians could continue to use the Serbs as cannon fodder just as they had in 1806-1812 Russo-Turkish War. Depending on how things go, the Serbs might be able to demand the terms of Ičko's Peace TTL as well, so that much might still remain the same. But the big thing is that Karađorđe is likely to work on consolidating his position as Grand Vožd. This could actually cause issues with Montenegro later on, especially if the Montenegrin court maintains a position of "we're the ones to unify the Serbs" as it did OTL, since I could entirely imagine a scenario where, post-secularization, a unification proposal between the two countries fails because Karađorđe's successor is unwilling to allow Danilo I Petrović-Njegoš to take his position as head of state (so we kind of end up with two dynasties fighting anyway).
Of course, my point on Russia could be entirely mute if this scenario was paired with a "France and Russia maintain friendly relations instead of fighting" scenario (reminiscent to TRH's
Marche Consulaire), but that might be going too far.
On the topic of language, honestly, in a Russophilic Serbia and Austrian Bosnia scenario, I don't think Slaveno-Serbian would win out - mainly because it is a construct of the Habsburg Serbs, developing out of the literary linguistic developments in those areas. I honestly think that Vukavian Serbian actually has a higher chance of winning out TTL. Miloš Obrenović resisted the adoption of Vuk's Serbian because he viewed it as too patriotic, which was something that would have not added him politically with either the Ottomans or the Austrians. Karađorđe and co. would very likely not be as resistive, and the Russians would be all on board, especially since it could enable the further development of public education, since I think Vukavian Serbian is more accessible (plus with the territory Serbia's going to control, it just makes sense).
However, in turn, just because Vukavian Serbian would work out TTL, doesn't mean all developments associated with it would. Vuk would very likely not spend as much in Austria, since he wouldn't have much reason to leave for Austria with a victorious Serbia, which might actually end up changing how his Serbian reforms actually turn out. He might not even meet Jernej Kopitar, which I think is a massive PoD in of itself! Sava Mrkalj might remain a presence, meanwhile, along with Old Rashko. And more importantly, as has been noted so far, this means there would be less opportunity for Serbo-Croatian collaboration on language, which may result in Croato-Slovene collaboration instead. Frankly, I don't think the Illyrian linguistic conceptions have any chance of working out, especially with Jernej Kopitar around. We could end up in a scenario where Slovene, Čakavian and Kajkavian are lumped into one language, Croato-Slovene, and Štokavian is split between two languages - Serbian, which would be largely Ekavian-based (assuming Montenegro doesn't become the dominant partner), and Bosnian (following Croato-Slovene reforming principles, and with Latin and
Arebica as writing systems - I could in turn imagine an earlier manifestation of the rhetoric of 'Bosnians are just Muslim Croats'), which would be Ijekavian-based - with some cross-pollination between the two (sorry Ikavian, it's hard to fit you anywhere).