I've considered commissions many times, I go back and forth on it. I wouldn't want to put a commissioned story into a "Year's Best" anthology, just because I truly want it to be a "Year's Best" -- i.e. I need to evaluate ALL the stories published to the best of my ability and choose the best regardless of name recognition.

I could commission some and create a new themed book separate from the "Year's Best", but that's hit and miss. The main issue with commissions for me is that you never really know if the thing you're commissioning is going to turn out how you want. If the authors are well-known it will probably be good, but I've had many editor friends commission stuff that was just phoned in.