Trezor is at heart just a secure display with a couple of buttons and a small CPU. Such a thing has massive applications in all kinds of areas outside of Bitcoin. If they can scale up and get the costs down, stick and slush could build an decent sized business just selling these gadgets to businesses that want strong authorization of certain actions. Any company that currently uses 2-factor authentication for logging in could potentially benefit from the upgrade - including banks!
I think it'd make sense to pursue such markets, even though they aren't Bitcoin related. The money made from them can always be reinvested into other Bitcoin related research, and making the rest of the world more secure at the same time is a clear win for humanity.
There are probably many specialty crypto applications where Trezor would excel, but for 2-factor Yubikey pretty much owns that space already. Tough to compete with a $2 (cost) USB plug.
Yubico has shipped millions of YubiKeys to more than 40,000 customers in 120 countries around the world..
http://www.yubico.com/about/reference-customers/ YubiKeys are JUST for securing an online account. A Trezor (or Bitcoin client) could act as an identity in of itself! It's not 2-factor authentication but a single source of authentication that can be identified and tied to a Bitcoin public key.