Unfortunately, whilst it is a 'good idea' and in fact an idea that has been put forward many times in the past, it seems that new upgrade paths aren't part of the plan.
If they can't (or won't) implement a new faction then this at least would give some new interest to the game. When Veteran servers were new, they attracted a lot of interest from many players. Quickly there grew a group of players who could dominate that type of world. World Championships also developed from a general interest group to a small group who dominate every new World Championship introduced. (They may be in a small number of alliances but it usually breaks down to two main groups fighting it out, the same players most of the time.)
So, new worlds, new features within worlds have managed to keep the game going so far. New features for units, if we can't have new units, would be most welcome!
I also like the idea posted elsewhere of going back to an earlier style of world without POI. I think you probably have to maintain having a fortress, to give some idea of a 'won world', but no POI, no HUBS (or a world with them dotted around veteran world style but not quite so many, just the normal 8).