I'm working on and off on a 3.0 version of the CEP. More of my time has been focused on our PMCE pack for 3.0 (
http://smashboards.com/threads/pmce-complete-extension-package-2-update-is-live-enjoy.339583), which is actually pretty close to being done - at least, the 10-stage expansion we have now. That doesn't count the 2 separate Castle Sieges that we did.
I'm thinking for this release, I'll take out the SSE and Brawl- stages, except for SSE: Jungle from the old P:M 2.6b demo. In it's place, I'm adding that How To Play stage from SSB64, plus some more Brawl stages like Mario Circuit (since it's gone in P:M now), Spear Pillar (STGTENGAN_1 is the only one that works over expansion, I think it's Dialga?), and Mushroomy Kingdom (again, only the above ground one works.)
The reason I'm doing this is not because these stages are good, necessarily - it's so I don't have to maintain two versions, and (maybe a little bit) so I'm not favoring certain stages over others. I posted all the SSE stages from my last pack to a single entry on BrawlVault, so they should be easy to get and add to your setup if you like them.
Here's a pic of my new SSS layout:
Ignore the two Green Greens icons for now - the second one ought to be Brawl's training room.