Simplifying Prestige Classs and High Level Play

Here's an idea: Basic Classes simply end  at Level 10. Introduce Prestige Classes for Levels 11 to 20.
ex. Archmage, Prerequisite : Able to Cast 5th Level Arcane Spells

There's always paragon path style. What other ideas have we got?
Some players would still want to continue their base class past 10th. Not everyone wants a prestige class or paragon path.

In memory of wrecan and his Unearthed Wrecana.

I'm not a fan of Prestige Classes all together. I prefer the class kits from AD&D 2nd Edition, where you choose it at character creation..

I also prefer old style multiclassing; where you have to choose to do so at character creation.

I won't mind seeing Prestige Classes as an optional module though, as I would hope the version of multi-classing I like would be an optional module.
They didn't seem to want to give us interstigñg high level classes. I was thinking a Wizard 10/Archmage 10 would effectiively be a Wizard 20 anyqys, so why make 20 wizardd levels?