Actually… the top keys stat can deliver that kind of info if I recall correctly. I’d actually intended for this kind of use case. I think if you dive into the memcached binary protocol request of stats topkeys, you’ll find that you can get a larger list of topkeys including deletes.
It’s not in the admin console and I don’t even remember if it’s in the REST interface. You may want to dig a bit @Crafty33 if you’re up to it. If you need some further pointers, let me know.