There has been discussion of using the genesis block hash to identify chains in BIP 21 (bitcoin:// URI scheme). However, this does not allow identification between blockchain forks building upon the same genesis block. While many see this as undesirable, I think it is inevitable that this will eventually happen at some point, and think it is best to build systems redundantly.

I propose identifying blockchains for BIP 21 and any other relevant needs through:

1) the genesis block hash for a new chain, or
2) a hash of the genesis block hash,  concatenated with block hash(es) of fork point(s) for a fork chain

This would support forks, forks of forks, forks of forks of forks, etc while preserving a fixed length chain identifier.

If a user wants to specify "whatever chain is the longest with PoW", they would use (1). In times where multiple chains are coexisting and being actively mined, a user can use (2) to specifically identify a chain.

Thoughts?