I definitely like the idea - and we are working on something super secret and super cool along these lines. The new "hero" will be radically different from your main hero - and well - this is where the Magic in Dawn of Fantasy will come into play, so you probably can guess what this is all about.
The new unit will be accessible for a one time purchase of ALOT of influence, but will be as powerful as your high level hero.
If we manage to fix OOS issues quickly Joseph might have this ready sooner than you think.
In addition we plan to buff up the current heroes as well with ability to learn more skills and perhaps even magic spells down the road.