The Bitcoin blockchain is already too big to download. Electrum figured out how to use specialized servers that index the blockchain:
Instant on: Your client does not download the blockchain. It uses a network of specialized servers that index the blockchain.
http://electrum.qc.to/It is open source..
Yeah Electrum is a thin client implementation. The issue with this is you need a strongly secured network BEFORE these get put in place. Without the pre-existing network security it hugely damages decentralisation, as these clients basically just steal the information they need to maintain balances, and give back nothing at all except extra network traffic. Even PoS staking secures the network, but without running a full node, I don't think this is possible.
It even says on their website:
Musicians and other digital art producers can prove when they created their work.
Looks awesome!