I keep seeing all of these "raise the level cap" threads popping up every once in a while.
They implemented True Rez because of some of the reasons that Chai listed. There probably won't be another level cap increase. And if there is, what are they going to do about TRs? When would you be able to do it? Would you have to gain the new cap befoire TR'ing, or would you still be able to do it at level 20?
Not going to happen folks. And if it does, it will ruin the game.
To this respect the Epic level handbook mentions that getting to 21 is a special time for the hero.
It suggests to the DM that getting to 21 is hard and doing it by xp alone may be too "mundane".
Thus attaining 21 is a "transition" to be accompained by a "suitable event" such as a holy quest, etc
In any case, the epic toon would be playing on realm of legends.
Things like that, TR alone looks too soft to be your milestone, since past lives are just that and not imply you become a legend.
Most likely TR may remain unchanged, since lv 20 is the cap for non-epic levels, beside reincarnation is originally meant to turn you back to square 1.
As for epic dungeons for epic toons, one gotta keep in mind that first new content would be made and second a new progression/mechanics would be made, and third, balance is already fragile on regular levels thus balancing epic would be as difficult as in PnP.
Actual quests however, need not be complex, and they are a pain in PnP only coz a DM would try to run everything at once and keep track of dice is a nightmare (unlike by computer).
Truth is the challenges are too epic that you probably get to face them one at a time just as in the epic raids we have now.
Resolving an epic battle is also a matter of having or not having the right power to beat the opponent, since you can't count on any of the numbers, be it bab, ac, saves, stats or whatever, them being all off scale.
The party probably would be more involved in finding a key artifact than buffing up for face to face combat.
Not to say that by the end of the day there would not be some epic monster being kicked below its tail.