My notes so far:
-in the wizard it doesn't show trezor unless it's plugged in first -perhaps a warning to plug it in?
-when multibit is opened it asks for a password -it's not obvious that the trezor should be plugged in
Does multibit allow restoring trezor seeds somehow? Or updating firmware?
Is an extra key put on the trezor for encrypting the backup and unlocking the wallet contacts/history or does it use some type of private key signing?
Thanks for the feedback. I'll try to address your concerns as best I can.
The Trezor capabilities only activate when a Trezor is plugged in. We felt that most folks would not want to be concerned with Trezor info if they didn't own one and that those who did would just attach it at some point. Also the password screen is quite crowded already and having a "Please attach your Trezor now" message would only be useful the first time.
We deliberately stay away from firmware updates because that is really the purview of SatoshiLabs and if something goes wrong during the process then we would rather they handle those situations with their expertise.
Loading a wallet with a seed phrase is possible for us to support (we provide command line tools in the MultiBit Hardware project for our own purposes), but this breaks the security model. Once a seed phrase is exposed to a desktop machine it is susceptible to malware which is the whole reason for our Trezor support.
Of course it is possible to go from a "hard" wallet (Trezor) to a "soft" wallet (seed known to desktop). This is necessary in case the Trezor is lost, stolen or damaged. But to go the other way would introduce a false sense of security. Rather than continue using a possibly compromised seed phrase it is better to simply create a fresh "hard" wallet on the Trezor and generate a fresh receive address. Then type the old seed phrase in to create the "soft" wallet, wait for synchronization to complete, then use the Empty Wallet tool to spend all funds to the new "hard" wallet.
The local wallets are encrypted using symmetric encryption from the Trezor device. This encryption is based on the private key of the seed phrase and therefore requires the Trezor to be physically present to unlock the wallet. In this manner you can safely use a MultiBit HD installation on another desktop machine and after you exit the wallet the data is encrypted such that no-one else can access it without a Trezor device loaded with your seed phrase.