Other thing that can happen is countries banning the use of bitcoin or actually holding any coins or in online wallets.
This is very classic problem, and the issue of segwit vs BU will always appear in search for a solution to this, it will always mempool flooded in the future if there is no clarity about the size used in each transaction, but don't worry because it is still far from our estimates, now segwit already sought 2-4 mb size for each bloksize