Can we focus on what Metagross can do, instead of what it can't do? Let's try to find some good cores for Metagross to fit in, and how its most effective set would look like.
Took the words right out of my mouth...
Truthfully, I think almost all of his usual sets will still be seen in great success (as they are not dramatically changed) and that he then functions as an interesting, if albeit, limited pivot. Truthfully I think his greatest strength will be fitting in cores that will be able to counter act what he needs help with and being able to solve what they need help with. Personally I would love the idea of seeing him be able to do this in conjuction with a great many things (I like the idea of him being a Pivot alongside Mandibuzz/Hydreigon as stated previously) so I wonder how well this would be then:
Lefties
-SR
-Meteor Mash
-Earthquake
-Ice Punch
The moveslots can be debated a bit, but with a reliable defog user and a SR setter, the two can perform a great combination while doing what is needed. Mandibuzz needs Rock, Electric, Ice, and Fairy weaknesses covered and Meta covers three in typing alone while hitting all three with his Steel STAB alone. Meta is weak (as been stated by one guy
SEVERAL times) to Dark, Ghost, Ground, Fire. Mandi is able to cover three of those (that's coincidental) and can easily work to covering the Fire weakness. Course this is something Meta could already do, so who could he then help later?
I'd like to say Jellicent, as he is able to absorb the Shadow Ball, the Bullet Seed, and the like. Is it a perfect combination? No, but I like the looks of it. Who else would be a good partner to help the Super Computer?