Hello Mageia and Mandriva users..
The beginning of your thread caught my attention and other developers at Unity Linux's attention as well. I can't speak for the other developers at Unity Linux but I'm pretty sure they may share a similar view as I do.
We do not see ourselves as a end user distribution and at the current time we are kinda in a gray area to be called a fork. Let me address both of those.
Not being a enduser distribution, but a distribution as a "Core" or trunk for more advanced Linux users to base a personal or community distribution off of. I personally have no desire to adopt or take in anything from Mandriva other than a few packages and draktools and those quite frankly I will import (patch and work with) until a better alternative comes to the community (as being a PyQT guy I'm not a fan of PerlGTK). Now granted our packaging style is a lot a like and we even import packages from Mandriva as it's our closest relative and what we're very much familiar with as a lot of us have learned to package on Mandriva or package for a fork that was heavily related too Mandriva in the past. So we have adopted rpm macros that Mandriva uses which makes it a little hard to import some Fedora and Suse packages with out a little more change than normal to spec files. However that hasn't stopped other packagers and I from pulling from other distributions. We have our own Kernel, Xorg, Tool Chain and KDE packages etc.. If Mageia was to fail horrifically and Mandriva was to go away we would still carry on, maybe tweaking some rpm macros to play more nicely with Fedora and Suse, but at the most it would only be a hiccup in our own development. So I personally see no need to worry enough to take on such a large task that would place our focus on a gaol and a direction that Unity Linux is not and was never planned to be. It's not like it would be something we would need to do too "survive".
Will we work with Mageia, Yes. We will have no issues importing some packages we may need (when/if there is some) and if there's any patches or fixes that are not applied we'll push the changes back up. However, our plan is the pull from both, if we need too, so we will extend the same courtesy for Mandriva. We each have our own individual feelings about the fork, personally I don't work with a lot of packages that are based on Mandriva for my own branch (or distribution based on Unity) called Synergy I use my own KDE 4 packages and take in a lot from Fedora, Suse and Chakra. I guess the only thing I follow closely that are Mandriva Packages is Colin's work on PulseAudio which I have no issue taking his current patch set and building Unity PulseAudio packages.
My point is we like Unity Linux the way it is, we're pretty flexible, we have a lot of tools that make our Job easier, but there's no need nor want too maintain any branch of Mandriva, more than just maybe pushing a few fixes up the pipe. We have a different purpose and goal, but we wish Mandriva and Mageia the best as they both in the future may make our jobs easier ;)
Hope that kinda clears things up ;)