That as a possibility is implicit in my thoughts, I'd say, yes.  

I am not saying it's the only way forward for Bitcoin.  I also think a block size increase is possible, though may be hard to do from a political standpoint.

It kind of HAS to be one or the other of those things.  And if it is the former than it follows that transactions managed off chain will be how the majority of transactions take place.  Either as Finney suggested (though I do not see that the "banks" have to create a currency... they could instead just let you trade "bitcoin" on their private ledger) which is a trusted model, and/or using trustless models like lightning.  Or some other invention that is one or the other or in between...