I like the idea. Randy clearly has a big re-write on his hands ATM and maybe has other priorities too. It'd be nice to have the new features and any little bugs that may have been fixed along the way sorted out too. I assume, however, that some of the bug reporting that would necessarily be generated would be incompatible across the versions and perhaps unwanted/ unsuitable bug reports may be posted by people. Not a huge issue I suppose. There would also be the problem of people DLing and getting confused with which version they should be using for stuff. Remember that ver 1.22 still sometimes causes confusion.

Again, not enough to prevent it being done IMO. All that being said, I still like the idea of an "official unofficial" build.
What would happen if the unofficial version included a feature that, for whatever reason, Randy didn't/couldn't/wouldn't include in the official build? We would then have an unofficial version that had a feature that some people (presumably) wanted, but a newer official version without the feature. Would future unofficial versions continue to try and re-write the code in - and thereby do something out of step with the official versions? Would it be left out? Is there the potential for Zdoom and UZdoom to fork at some point?