I don't see why not. I'm guessing for a majority of the school attending/working people, Sunday is an infinitely better day than Tuesday. Keeping it at 7:00 server time is a given. Also, Sunday and Tuesday are both GvG days so there's a sort of symmetry there that isn't broken by switching from Tuesday to Sunday as you suggest.
However, if any change to this actually happens, it'll be after this coming Tuesday's test run.