The main problem I see with this is how to EV your pokemon properly. In particular, the speed tiers would be shifting constantly. All of a sudden, your once-reliable revenge killers are outsped an KO'd by the threats they used to counter because people started realising how great they are. Similarly, defensive EVs would need very careful consideration, especially on walls that usually split their defensive EVs like Ferrothorn. You'd have to change your EVs all the time to make sure that you're not being 2HKO'd by important threats. Yes I realise that the metagame would settle after a while, but it would still be way more chaotic than the regular OU metagame. Just look at the Smogon statistics for each month- there are always a bunch of pokemon changing places and moving up and down tiers. In a metagame where the pokemon's levels are being constantly adjusted, small changes in popularity cause the levels to change, but maybe only by one or two. But maybe those couple of levels are enough for it to get some vital 2HKOs, or to miss out on them. This would prompt other pokemon to change in popularity to accommodate for it, and then their levels will change, and so on and so forth. All in all, I don't see this metagame being very stable or practical at all.
That's all I have to say.