or maybe a hardcore fps in a high fantasy setting
oh wait, that was called shadowrun and it sucked
I thought it was called Hexen and did pretty well?
Heretic and Heretic 2 (though that's a Raven property, not id) had the whole fantasy setting going too, and more recently there were Wheel of Time and Dark Messiah Might and Magic.
All of which are very playable, though I enjoyed Hexen 2 and Heretic 2 most of all.
As far as the OP goes... Carmack's interview with Kotaku
"And working with other companies hasn't been working out as spectacularly as it could. So the idea of actually becoming a publisher and merging Bethesda and ZeniMax on there [is ideal.]"
Perhaps it will work out, but I don't see how an acquisition is that different from "working with other companies", aside from changing the option of "get angry with your distributor and break out the lawyers" to "get angry, get told to suck it up, then quit citing creative differences and leaving your IP behind".
(Edit: Layers --> Lawyers. Either way I guess you still end up screwed)