This topic was already discussed back in May. There's no need for payment schemes or other complexity.
I will add something to the scalability page about this.
From my reading, the proposal in that thread was more or less the same as mine, and an argument against it were that nobody has to download the entire block chain because they can just rely on the compiled-in "checkpoints". Of course, 'supernodes', i.e. miners, would always need the entire chain to be able to validate transactions.
But even if my client has a checkpoint, if the size of blocks is 1 MB or more (which it will be eventually), it's still not practical to expect clients to ever have to download full blocks on an ongoing manner; end-user network bandwidth does not support that. They will need elided (pre-pruned) blocks.
Of course, it's possible that there never will be enough transactions on the bitcoin network to make blocks this big; I strongly suspect that bitcoin will never gain foothold except as a currency for pseudoanonymously buying illegal goods or making untraceable payments for legal goods that the end-user doesn't want associated with them (it is the only monetary niche that I can see that bitcoin has advantages over other forms of payment), and maybe the number of transactions per second in that niche market will never exceed 10 or so ...