Usual caveats: stream of consciousness, just spitballing.
Almost every D&D session I have ever been a part of has happened between levels 1 and 10. Probably 85% between levels 1 and 6.
I would like to limit levels to six, and somehow else grant magic and other cool things in other ways.
In 3.X the feat system and assigning XP values to new feats allow for a good transition from levels to an ad hoc skill based system.
There is a lot to like about low-level 3.X. But there’s a lot to love about B/X style play too.
It’s probably going to take a lot of work to wed these two ethics into one coherent game, but I’m sticking a pin in it to tackle it “someday.”
Here's a link to the original E6 document for your perusal and possible use!