I play a lot of Ubers where mega-Scizor is one of the most commonly used mons. However, all Ubers sets run Toxic (due to a lack of steel/poison types, a lot of bulky mons that you want to wear down with Toxic (and it's easier because a lot of them don't carry lefties, like bulky Arceus formes).
Just out of interest I've been messing around with a Toxic support mega-Scizor in OU and while it isn't excellent if played well you can predict a Steel-type coming in and U-Turn out (the issue is that you get 4MSS and if you want to run U-Turn you have to lose out on one of Toxic, Bullet Punch, Defog and Roost, all of which are pretty important. Otherwise you can just double switch if you're confident your opponent will go for a steel).
Would anyone else say there is any use for Toxic Mega-Scizor in the metagame?