I went over the side menus in WMT and didn't find the "change of address" tool there. Have Google removed it? If so, is there any other decent way to inform them of any domain change?
It's still there and hasn't moved, at least for me, and it feels like a strange thing to AB test. Make sure you're in a property and click the gear button in the top right.
Here's a direct link to the tool where you can select any of your added and verified properties: