I think it does not make sense to try to get this standardized for
current Bitcoin transactions. They are just too complex.

What might be interesting is to have something similar for Segwit and
Lightning transactions.

* TREZOR performs extended validation of the inputs, when all of
prev-txs are streamed into the device and validated. Your standard does
not tackle this at all and I don't think it's worthy to make this
standard unnecessarily complicated.

-- 
Best Regards / S pozdravom,

Pavol "stick" Rusnak
SatoshiLabs.com