Motivation: Many real users want to merge many UTXOs. The current method of doing this using many SIGHASH_ALL signed inputs has a quadratic scaling cost to verification, which makes block time validation expensive, and causes a worse problem for GetBlockTemplate calls which process the entire mempool. One improvement to this situation may be to give users a tool to create cheaper-to-verify transactions. (This doesn't help against malicious users.)

Proposed Solution: A variation of bitcoin/bitcoin#6482 in which @gavinandresen proposes a hack to create many-input transactions which are efficient to verify. The hack introduces some subtle security-vulnerability edge cases which must be addressed if we were to adopt this approach.