Since you're pretty new around here, someone (I guess that'd be me) should explain that WP is not like "most other" open source projects. Sure, the code itself is open source, but that does not mean development is. The developers, and the main guy Matt, particularly, have a vision and plan for how they want WP to develop (and consequently WMPU, which follows the WP code).
Donncha is the only guy who updates the WMPU code. Sometimes Matt does, or I think he did in the past. There is a bigger group of people that work on the main WP code, maybe half-a-dozen, tops. (I'm not sure, someone feel free to correct me on that). That is it as for as coding goes, and that is how it will remain, as has been said in Matt's blog, on wp mailing lists, on the wp.org forums and many, many other places around.
I can tell you are really eager to help out though. :) You should read this for ways you can help, if you haven't already:
http://codex.wordpress.org/Contributing_to_WordPress
Even thoguh it is mostly about the regular WP, Mu is really just a branch and the same applies here.
Also, I should point out the above is just my own opinion and impression from the past year and a half of being a WP user, an MU user, plugin/theme developer and support forum volunteer.