Honestly, Ditto strikes me as being extremely overhyped. Sure, if you go against HO or someone willing to mindlessly SD/DD against you, it's good. However, looking at the top 50, the setup sweepers I see are SD Scizor (lock yourself into Superpower, please), DDNite, Terra (just play it like CB vs Ditto, or sub if you have it), Lucario, Conkeldurr, Virizion and Cloyster. There's maybe two mons there I'd be bothered about having Ditto against, and more often than not, it's going to do no better than any other random scarfer. Not to mention that almost all of these have a move capable of hitting Ditto hard on the switch, so you've got to be extremely careful about switching in in the first place.
So, what does it offer outside of revenge killing? Not a lot. If you try to use it vs stall, bearing in mind that you're only really going to be using Ditto on more offensive teams, you're just asking to lose. I'd quite happily let people use Ditto to try and Spike/Spin vs me, as any full stall team is going to carry either a spin blocker, or something like a Tyranitar. Either they Spike, and you get an easy Spin/switch to whatever to take advantage of choice locked Spikes, or they Spin, and you block/Pursuit it.
Basically, I'd much rather use a normal Scarfer that will be consistently useful outside of revenge killing (i.e. Landorus, Rotom, Jirachi, whatever) 95% of the time. I really wouldn't be surprised to see Ditto drop to UU once the hype dies down.