I confirm it works with my homemade (but full compatible with stock firmware) Trezor, at least for signing outbound transactions.
I can make more tests if needed. The software used is Electrum-DASH 2.4.1.
As far as I know -walletnotify option runs user script when the daemon sees new transaction with one confirmation.
What is right way to receive InstantX transactions?
I doubt it is fresh idea but how about storing hashes of SSL certs in DASH blockchein?
Masternodes could help browsers with instant cert validation then.