I like the UUID-as-path idea. That resolves the problem of how to share the alt-chain merkle tree quite nicely.

On Mon, Nov 4, 2013 at 7:16 PM, Peter Todd <pete@petertodd.org> wrote:

No sense in compromising - you need a whole merkle path to prove the
extra data is valid so you might as well make this a full 256 bits;

The Merkle branch doesn't get stored indefinitely though, whereas the coinbase hash does. The data stored in the coinbase [output] can always just be the 256-bit root hash truncated to less.

I doubt the additional bytes make much difference really, so the additional complexity may not be worth it. But it wouldn't be an issue to do.