As I see it, there are three ways to do epic.
1: Integrate it tightly from the beginning making it into a complete whole, a single rule-system where you can get eaten by rats and defeat the gods in fair combat, the only good example I can think about right now is the Disgaea series.
This would mean coherent rules from beginning to end, level 20-25 is no different in power curve then 15-20 was (the curve should be exponential though, you should never, ever feel a sense of diminishing returns, that's exactly where boredom lies).
2: Make a super-world of some sort, yes, this would include exalted, the world of darkness or any other such thing, doesn't matter, as long as there is a proper reason for the two to be seperate.
This would be best served by tiers of power, meaning that, yes, you are in fact level 1 when you breach the shroud, however, this doesn't totally exclude the possibility for normal levels to be higher than 20, just that level 20 in a single class is the mortal cap.
Non-epic resources would be assumed trivial in these worlds, so, indeed, teleporting is definitely the common way of transporting.
3. Don't, stay away from it and accept that 20 levels is enough for this game (not saying that it's true).
1 is where 4th ed went (or at least tried to go to an extent), personally, I thought it was pretty lacking since it was to strict and I love loose systems.
2 is really counter-intuitive to how dnd works, it's quite simply much easier to not have to micro-manage resources at that point so it might be hard to do it well.
3 Gives little hassle but is less impressive.
My gut tells me that executing an epic system which fits everyone's tastes will be quite simply put, bloody hard.
When you have characters who are used to having power over life and death, teleporting, travelling between worlds and wrestling adult dragons, should there really be more?
If you can do it, kudos, my point is just that I've seen what a monumental task it is to create an adequate experience for all people involved, and this is just not with pen and paper RPGs, even games such as Diablo only work well for a small number of people once it passes a certain level (I hate it past nightmare for instance, my GF can't even stand nightmare).