That just means it makes more sense to me for the Romans to make the Zagros mountains as the border then. If the Ottomans break through them then have to march through the Syrian desert or go along the path the Romans can be assured you’ll take so can make a string of fortress cities that can slow down any potential invaders coming that way while you march forces that way. The Russians have General Winter, the Romans can have Stratagos Sandstorm. Or something appropriately Greek. Make the Ottomans turn East anytime they’re in the mood for war because they don’t feel like killing themselves in the desert.
The problem his that you'd have to take all the cities in the Zagros themselves, and that's a big hit on the viability of an Iranian state, taking cities like Kermanshah, Hamadan, Shiraz. Alternatively if you aren't taking the big cities, you're taking and fortifying smaller locations like Yasuj, Kazerun and Bandar Bushehr (and others) scattered through Zagros. For an idea of how big a deal that is (and how defensible these locations would need to be made) - Yasuj is 200 km from Isfahan, one of the great cities of the Ottomans, and less than that from Shiraz. Those are "if the Romans attack, its existential" borders, even accounting for some defensive advantage from finishing the journey to the Zagros.
I doubt we'll see that sort of border though, since we're talking about basically annexing Mesopotamia and a bit. It'd probably include Kermanshah to guard the central passes, and then follow the Kharkeh river to the Tigris, leaving Basra as the southern focal point of the defence. That's still be one hell of a victory.
I really hope he doesn’t. I don’t want the next 50 years to just be Khosrow the second 2, electric boogaloo. I actually think it would be more interesting if the Ottomans and Romans decided to try and make a lasting Alliance out of this situation with the Romans funneling then equipment and men for some Eastern conquests. Ottoman Uyghurs would be pretty awesome if the got far enough into the North East
"Great Crime", "He is my vengeance" - I'm not sure that it'll be a long-term alliance, especially since B444 said he likes the Ottomans as a constant foil. I agree it'd be nice though, and potentially plausible if it didn't leave the Persians and Turks humiliated and with a deeply wounded pride.
I think what we're likely to see is a sort of D3-without-war leader, especially as a listener. Romans take substantial parts of Mesopotamia, and then let Iskandar loose on a fractured and weakened Iran to perpetuate the war as a civil war, and then Iskandar wins and starts applying the military and economic reforms of D3 to Iran, essentially creating a fiscal military state there. At best the Romans have bought a generation or two before revanchism becomes too much to ignore and the Romans find out how brutal it is to fight on that border I described above (basically hard to defend, harder to attack from, hard to attack it - see the war between Iraq and Iran for context).