The MimbleWimble design [1] allows inputs to be cancelled against the outputs they spend, with no loss of security. Essentially, the entire blockchain history may be collapsed to a single mega transaction, with all coinbases as inputs and the UTXO set as outputs. In his recent talk [2], Andrew Poelstra discusses the achievable savings relative to the bitcoin blockchain.

[1] http://mimblewimble.cash/20160719-OriginalWhitePaper.txt

[2] https://www.youtube.com/watch?v=ovCBT1gyk9c