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I've recently looked into Plone quite a bit last summer. I really liked it a lot, but ran into a wall trying to deploy to a shared hosting environment. I forget exactly what it was, but there was some process that needs to be running and even with shell (not root) access I couldn't get it set up.
It's a great system though, if you have the capability to run it. If you learned PHP, Python shouldn't be too hard. It's pretty nice.
Regarding creating a module for CMS for Xoops, I'd suggest looking into it more as a packaging of Xoops. That is, we configure a default install of XOOPS with articles and news and blog, etc. configured in more of a CMS style, as opposed to the regular default install which is community-oriented. We may still need some new modules to handle history (revisions), etc., but to a large extent, I'd see it as a packaging effort.
I'm very interested in the CMS side. I go round and round trying to find a system that offers good flexibility and features but also provides a relatively painless way to manage a 'regular' (non-community) web site. I like XOOPS a lot and believe it has a great foundation (the code isn't as scary to look at as many out there). A CMS-oriented packaging would be really nice I think.
-Tom
NOTE: I'm NOT talking about a fork! :O