I haven't commented on this issue before because I can't really be helpful. I just don't understand why hg is being considered before it's Windows support is roughly equivalent to svn and cvs.
Is it really that you don't *understand*? It's fairly easy: there was a PEP which offered a number of options, and there was BDFL pronouncement. This (BDFL pronouncement) is how Python has always worked, and, as a principle, it is a good and useful process.
Now, the specific outcome of the process means that more work needs to be done. So we have a *second* PEP, and we have a lack of volunteers that help implementing it. The second PEP hasn't been approved yet (as it isn't complete, yet), so migration to hg is stalled. The primary volunteer (Dirkjan) has indicated that he can't help with that specific issue, so other volunteers need to step forward, or we cannot move to hg.