This is not a problem and never was. OP, go read the white paper and the developments in the dev subforum. This is what happens when n00bs spend too much time in Speculation and not enough time learning about the bitcoin protocol itself.
We get a thread whining about scalability at least every month.
1) You do not need the entire blockchain
2) Blockchain compression
3) Big hard drives. When I was a kid people had 32 megabyte hard drives. And again, you don't need the entire blockchain!!!
4) Lite clients that require 0 trust using some devious merkel tree tricks
5) Read the fucking available material on the problem already, smart people have already solved it.
About point 1.
I assume this is correct but imo there is no simple way to determine what can be deleted.
They cannot purge transactions older than X years since this might kill peoples offline wallets.
You can only remove transactions to accounts that now hold 0 BTC but that might give the spender free money again.
The only way you could pull it off is by making a 5year checkpoint every 1st of January, in which all the balances of blockchain accounts ever used are stored and only transactions from that date forward are processed.
I see a lot of problems with your point 1.
P.S. haven't read the smart people solution but a link would be appreciated.