Sorry for the very late reply! Thanks for the detailed summary 
I’m a big fan of the unsigned TLV for SPV proof, very good idea!
It all looks mostly good to me, I only have a couple of nitpicks:
- C): I would like the outpoint to be included in the signed fields, it’s nicer for
txindexnodes and provides more information about the tx which is generally a good thing - C): I’m not a fan of the “hash of the SPV proof” proposal: I don’t think it’s a good idea to force nodes to be able to generate the SPV proof when creating the announcement, as I believe most nodes won’t care about including an SPV proof for light clients
- D): I think we could collapse feature bits 1 and 2 into a single one, I don’t think it’s a huge amount of implementation work to support both and would speed up network adoption. But I’m also ok with keeping them separate if people feel strongly about it.
- E): nice to have this!
On the eclair side, we’d be happy to work on implementing features 1 and 2 as soon as you feel that you have the spec ready and an lnd implementation ready for cross-compat. Let’s do this!