People will use marginally profitable hardware while the exchange rate keeps it that way. A 100% p2pool network would give more than just the marginally profitable too much variance to tolerate, I think I quoted > 1TH/s.
I understand what you're saying. If we're just talking about variance, then yes, I agree variance is a problem, especially if it forces a large percentage of miners to discontinue mining. But when it comes to controller hardware/software considerations, I don't think the variance argument really applies, because if tomorrow the protocol/software necessitated a slight upgrade in controller hardware in order to keep current mining hardware functional, I believe most would upgrade very quickly (if the choice is between turning your mining investment into a paperweight and spending a few bucks to upgrade the controller hardware, it's not a tough decision). The cost of controller hardware is and likely always will be a tiny fraction of the total cost of a competitive mining rig. For that reason, I still believe that the solution should not necessarily cater to any specific hardware configuration.
I don't think you understood what I was talking about wrt hardware changes. I wasn't suggesting a change to the controllers at all.