You've confused me with the last part. Doesn't SeedSigner need to contain seed or zprv in order to sign tx?!
I like the idea of erasing seed words each time you turn off power from your device, and then import them quickly with QR code scan that contains seed words.
SeedSigner, Krux and few other signing devices have non-persistent storage, so they don't really need secure elements.
Software is as much as hardware under that warranty, simply because it's only them who can deliver it.
Or you expect they'll change the Nano S for Nano S plus when people will complain that the LL no longer supports their Nano because the software is too old!?
So the important updates will be there.
Check out for yourself if you can still use their ledger live app with all of their many discontinued products like Ledger HW.1, Ledger Nano, Ledger Unplugged and Ledger Blue, than you will answer to your questions.
Warranty for many product doesn't mean you are going to receive updates in future, especially after production stops for this devices, it's rear thing even for smartphones.
If it doesn't support new address formats (I'm thinking of Taproot now), the hardware wallet becomes pretty useless.
I think they support Taproot address format.
Hardware wallets with Taproot support are Ledger, Trezor and BitBox02, and I know SeedSigner developers are also working on this.