I think latin empire part is unfinished at all.
you can create latin empire through crusade event, and seize territory from byzantine empire. there are several events to portray the divergence between frankishes and greeks. but no more any otherthings
Even if you seize all the territories and replace the entire Byzantine Empire with the Latin Empire, nothing will happen. The empire becomes an awkward foreign object in the game, detached from Byzantine related content (well, just like true them in history).
What you can do is just hybriding greek and 'restore the byzantine', then get a event "frankish empire crashed". that's quite strange.
I agree with that the latin empire need more extended contents. at least players should receive some feedback on their success along the hypothetical path, rather than making it feel like something destined to be born with only a failed ending.