OK. Is there a semi-official maintainer for Windows?

I don't think so. There are many Windows features (x64 port, threads + some fixes) which are forks during the long period of time. People who use them find these features to be working.

IMHO, it is better to have at least "experimental" features than to wait years for the stable ones. Any software system has bugs. The current Windows port cannot be spoiled by these changes, and SBCL community needs to be more open in such cases, encouraging people to merge the code, giving them the commit access, etc. The people who maintain Win64 forks could be excellent Windows maintainers, just let them get rid of the forks and move the code to the main tree. Maybe I am wrong here, but it seems to be the optimal way to boost the "SBCL for Windows" development and attract more developers.