A true example of making better use of available space would be the Mimblewimble protocol, which allows all spent outputs to be permanently erased from history.

A true example of making better use of available space would be the Mimblewimble protocol, which allows all spent outputs to be permanently erased from history. The integrity of the entire transaction history can be verified from the UTXO set and the history of transaction kernels (just ~100 bytes per tx).