I do wonder at the overall narrative of the TL, now that Rhomania has long since passed it's final peak under Niketas. The "Revival of Rhomania" had a great narrative thrust, with a suitably Roman self-limiting civil war. But where are we going now? The "Retirement of Rhomania"? A 4 century long decline into a comfortable second rank? That would certainly be interesting, but so far IMO there has not been much overall structure to the story, narratively speaking.
I don't know what Bas444 is planning - but I expect that there will be another great period for the Empire when line infantry starts to become a major element. Niketas had the rise of the cannon on his side, but we haven't yet seen massed gunpowder infantry (unless I've missed that).
The Romans are probably the first in the Mediterranean who would have access to this, or develop it. Once they start having line infantry to put against their neighbours, I'd expect a Niketas Reborn (if the Emperor is particularly good), or a very successful expansionist who brings North Africa and Mesopotamia into the fold as Despotates (perhaps S.Spain too, I forget who controls that, Arabia would be grand in the long run as well). After that, I expect that northern Europe, with their control over the new world, will start to outpace the Romans economically, with the Empire and the Despotates lacking access to the New World for resources. I would expect that the wars that the Romans get involved in with the new powers in Europe would be primarily defensive, rather than expansionist, turning to focus on the East Indies once again.
After that long period as a second-tier power that can project power in the Med and the East Indies, rather than additionally in the New World (and maybe India), I could see them become prominent again as those Empires start to crumble, oil becomes valuable, and they build a true Suez Canal. That would change the economic game in their favour, and add that to their touch and go control over the main trade routes in the East Indies is great for the long game.
The biggest factor IMO? The Romans have already gone through the stage of acknowledging they can't control everything from Constantinople - that respect of the need to decentralise and sophistication of governance may leave them to last, or be accepting of a federal model in the long term, which would reduce the rise of independence movements on themselves.
I don't see them as the number one power all the time, but more like a stalwart power. Sometimes eclipsed by Empires that burn brighter (like the British or Mongol Empires), but always persisting. Eventually reaching the point where it is one of the (at least 3) super powers, alongside China (potentially Indonesia), and an alt-USA (or Brazil).
