The Peloponnesian War would seem like an appropriate candidate for a future TW, don't you think?
To the Mediterranean culture sphere, it was like an ancient "world war" since, for the first time, all known regional powers where somehow involved in the decade-long struggle between two determined alliances.
My thoughts are: They often test new engine features in a somewhat limited fashion before bringing it on to a whole new level. This will (hopefully) be the case with current E:TW and the upcoming N:TW.
Now, with ship battles included, I could imagine exciting galley battles, trying to ram each other and all that.
On land, we would have mainly static phalanx battles with skirmishers and limited cavalry. We know this from past releases already.
Okay and with this game working, they could move on to the broader scope of the "Roman era" that's being requested so often.