Actually I have in mind a prestige class that has increasingly-difficult prereq's for EACH LEVEL, so that you might qualify for 1st-level ascendant (or whatever) but not for 2nd level. Some of the prereqs would involve major quests or accomplishments (yes, Tonguez, hailing back to the immortals set...) such as establishing a dynasty, etc. Of course the prereqs would vary widely depending on the character's path/desired portfolio, so it might be hard to work out.
Of course pcs who don't take this will be left behind; gods don't generally take mortals up to the new celestial palace with them, you know. But if you compare a character who has first-level domain spells vs. one who's just achieved eighth-level wizard spells, well... who can say who's better off! I guess it's going to be hard to make it a balanced prestige class, but the idea of taking 20 levels in a prc with suboptimal abilities (compared to adding 20 levels to another class, many of which will be epic) in order to achieve the big payoff will deter most pcs. Those who persevere through it deserve to win big.
When all is said and done, the trade-off is that the god character gets a lot less "action" cuz s/he's always busy with divine stuff... not dungeon delving and such! So the ascendant (working title) is not exactly for pcs who want to stay active adventurers.
Anyway, still under construction; thanks for the feedback. More??