I don't really get what you are talking about. Everybody has been doing MMIO for a while now (and by for a while I mean multiple decades), and IO is usually not

I don't really get what you are talking about. Everybody has been doing MMIO for a while now (and by for a while I mean multiple decades), and IO is usually not an issue in personal computers anyway; OOO, compute and the memory hierarchy is. We are not discussing about some mainframes...