Storage and internet bandwidth are not really an issue these days. The real issue is the CPU resources used during block validation. Every new block that a node receives has to be validated against the known blockchain. This includes blocks that a new node downloads for the very first time. Some idiots are still running nodes on Raspberry Pis or Beagle Bones. When/if we move to 8MB, these nodes will not be able to cope with the larger blocks in a reasonable amount of time.

If you run a p2pool node and bitcoin node on the same machine (like I did), you already see a problem today when 1MB blocks come in and you are running anything less than a 4-core current generation CPU. My solution was to run p2pool and bitcoind on separate i7 machines, which was a pain in the ass but my setup can now handle 1MB blocks without too many orphans of p2pool shares.