Here is an alternate history challenge create a situation where Rhomania falls before the 4th crusade, and another Hellenic empire takes its place. The only rule is the new empire cannot claim the title of roman empire.
Making Epirus that powerful without giving them Constantinople too early will likely mean that they need to expand into Italy, Croatia, or Anatolia. Of the three, Italy is the one I find most interesting, and in 1200 the Kingdom of Naples was having a hard time staying affloat. Butterfly Charles of Anjou and don't give Naples any other strong rulers . . .
Don't forget who rules (well, he's a minor as of 1200) the Kingdom of Sicily (no Kingdom of Naples yet).
OopsDarn HRE. If OTL's schedual holds, or the Pope wants to make a power play against the emperor (the Epirotes were often Catholic sympathetic when it suited them), then it might still work, but definitely more difficult.