Thanks to all for the replies!
I didn't knew about Expanded Mod, too recent for me, but it looks exactly to be what I was seeking - an "upgraded" SE4 set in the SE universe.
I knew Proportions, and quite liked it (maybe a little too slow to start..), will be a good candidate for another SE univerese experience with changed gameplay. Maybe Carriers Battles also.
Adamant and Dark Nova are presented as MP mod without custom IA, as I'm interested in solo play I think I'll pass.
For an universe change I think I'll have a look at the huge StarTrek mod (a favorite universe for me 'cause it reminds me of my youth

).
Edit :
Dizzy, I think I've seen a mod of you somewhere but can't remember where, nor what it does ...
Last note, I'm also waiting for SE5, has anyone a release date sooner than June ?