hmmm. maybe an option after initial install? you can user either the normal decentralized method, or opt to do a quick verify?
The issue is for 99.99999999999999999% of users given two options:
a) the right but potentially long and boring way
or
b) the super fast and easy ( .... and potentially cryptographically insecure ... they already clicked a).
I do think the protocol could be expanded to do it is a p2p fashion using the nodes.
1) New nodes compress and hash 10,000 blocks into a "macro block"
2) New nodes randomly pick one prior macro block (to date there would be 17 macroblocks) and include it's hash in coinbase
3) Old nodes would ignore this but new nodes wouldn't consider a block valid unless the macroblock hash in coinbase is valid.
Virgin node bootstrapping.
1) Node requests macroblocks from peers and records their hashes. (downloading all 17 macroblocks would take node to block 170,000)
2) Node requests newest blocks normally and validates macroblocks from the coinbases.
If all 17 macroblocks have valid hashes then the macroblocks are valid and thus tx are valid.
User could even download the 17+ macroblocks from non p2p source since validation is based on the blockchain.
