The storing of the entire "ledger" is one of the main problem with bitcoin, and really can only be solved by shifting to a time-based-balances summary.
The reason it takes bitcoin "users" 4 days to get started is the collection, unpack and interpretation of the blockchain.
Assuming by "users" you mean end users and not miners, Electrum has already started working on that, actually. Users creating a wallet do not need to download the blockchain to use their wallet. (Android support is super clunky so far, but it's a pretty neat solution to that issue.) Pruning resolved blocks is also a good suggestion, but the optimal solution is still going to be enforced minimum transaction fees.
http://electrum.org/