I've read a few of the discussions relating to migrating off-topic questions and haven't got to the bottom of why the list cannot be expanded beyond Meta and SO.
There's been a few observations that the need isn't there, but I'd beg to differ - I've come accross a few Windows questions. I can either vote that they are closed or flag them and hope that a moderator moves them to a more appropriate site. In fact, I'd (guesstimate) that I've come accross more Windows questions than programming ones. Oddly enough, I have an option to vote to migrate to SO but not to any other site.
Is there a downside to having some of the popular computing sites listed in addition to SO? Such as Super User and Server Fault? If there is a limit, then maybe swap SO for one of the other two?