I wonder if there will ever be an opportunity to start to replace the 1500 byte MRU / MTU across the internet. There are of course some jumbo LANs with ~9000 byte frame sizes allowed.
If we were ever to start making the change what would the next step up be? Up to 9k? To just under 64k? More? (I have this vague recollection that some protocols might start to break if we get near to 64k, because of field size limits, can't remember though.)
It's obviously a good thing if routers and switches have to process fewer packets per second. And ram is cheaper. On the other hand, long queuing delays are very bad, so sane queuing policy and good design would be a must, but then that's just another way of saying don't design things badly.
Of course, some use-cases would possibly want to keep packet sizes down because of real-time considerations. (Revisit the considerations behind the design of ATM.)
Somehow I can't see that 1500 bytes is going to be an ideal choice for decades to come, so perhaps now would be the time to start, saying that all new good Internet core routers should handle x byte packets. Testing might be a problem, as getting complete joined up end-to-end paths would be needed before experience could be gained from large-scale real-world field testing outside big labs with controlled kit.