Ottomans-So we are agreed, we attack India.
Rhomania-We are agreed.
Ottomans-Most excellent. [Deploys 100,000 to the Punjab. Vijayanagar counters with 250,000.] Uh, Rhomania, can you help me out here?
Rhomania-Sure thing. [Puts 9,000 men into Surat.]
Ottomans-Nine thousand, that’s it?!
Rhomania-Uh, yeah. Did you think I could put in more? Steamships won’t be a thing for at least another 150 years, dude.
Ottomans: I hate you. [Vijayanagar stabs them in the face.]
Rhomania. Mmmm, popcorn. [Munching sounds.]
This path would basically make the ruling Roman the Troll Emperor. I love it. Following it with an invasion of the Ottomans is also an option (even if it would mean no chance of co-operation ever again). However, I imagine that Osman has an idea of how the Romans would be providing significant help.
The Idwaits’ main defense, besides logistical/geographic issues of course, is that their territory is mainly modern Sudan. It doesn’t yield nearly enough to justify the expense of taking it over. But if they started cozying up to the Marinids or Ottomans, they’d get put on Constantinople’s ‘must kill’ list really quick. If the Idwaits are paying attention, they know this. But if Rhomania or Ethiopia decide they want to have a go at the Idwaits, they have a ready-made casus belli. Per the treaties ending the war, the Idwait Malik-ate owes both the Empire and Ethiopia an annual tribute. Let’s just say the Malik is behind on his payments.
It does have the potential to be a perfect 'practice invasion' for any innovations (primitive desert carbine troops?). New military innovations that would work in the Malikate would work against the Marinids or Ottomans in the future. (Plus, I imagine Carthage would love them).