I recently had occasion to do a test installation of XOOPS on my server. Talk about poetry in motion! It was effortless and a joy to behold. User registration was also smooth and, so far as I can tell, bug-free.
Quite a contrast with my initial installation of PhpWiki (and reinstallation and upgrade to 1.3.10 when the wiki went south after being Slurp!ed) a few months back.
I haven't taken the time to check for a statement of your main development goals at present so forgive me if I'm talking out of turn here, but shouldn't ease of installation and user registration & security be foremost?
I'm working on the configurator again
(it's even default on virgin setup), but nobody
helped so far, and it's not ready yet.
For easier user registration / administration we'd need also more work. Sure.
UserFile Management also. Currently we only have one huge upload flat file space. This should be made user specific.
Also database upgrades could be made easier, storing the db-versionnumber somewhere and upgrade only from this version to the current version. This would safe us from costly testing against all existing problems. Testing for db features is mostly more work than upgrading.
I have done a lot of work on testing, fixing and documenting security for PhpWiki - with major direction, input and help from Reini.