Unless I read this wrong you are talking about a re-writable block in the chain which is something that I have played with myself
and it is quite possible to hash some of the fields in the block whilst leaving the others open to change.

Good to hear people thinking out loud and if you think in terms of blocks in the chain not only expanding sideways but the
block-ledgers growing downwards then you are left with something that will scale but the credit for this must go back to bit-torrent
because they first came up with the concept of hashing hash's to bring us P2P distribution of files that does scale and even when
they take one server down others pop back up to take the slack so it's not really fully centralized.