Building a hardware wallet inside a smartphone is definitely possible.
It basically just requires two things:
- An integraded RNG + Secure element
- A second display + buttons for verification
With these, you can fully implement a hardware wallet inside a mobile.
You can use the mobiles OS / application to communicate with the hardware wallet and use the second screen/buttons to verify payments.
You would be fully secured against a compromised phone (thanks to the second screen and verification buttons) and you could also be secured against theft of the phone (through password protection with wiping after X wrong attempts).
I'm thinking along the same line. Perhaps the technology of dual booting available to PCs can be embedded into smartphones for the sole purpose of having the wallet secured from attacks and whatnot. While it's not feasible for most phone manufacturers, this will be a head-turner and a possible innovation for future smartphones that can act as a general communicating tool/device and another, distinct purpose aside from the conventional use of it.
The only attack vector i can think of at the moment is if your mobile is compromised AND it gets stolen afterwards.
In this case the attacker can gain access to your password + physical access, which is enough to steal funds.
I'd definitely love such a hardware wallet integrated into a smartphone (even though it still should not be used for large amounts -> 5$ wrench 'attack').
But it would secure people against simple malware (which definitely will become more 'standard' if the amount of BTC mobile payments does increase).
Having the phone stolen or lost will be negligence on the end-user's part, so that I think will be inevitable and uncontrollable, but I'm pretty sure no one in their sane minds would want to have their phones stolen so they would definitely keep it safe. As for the last passage/statement, I'd say this should be optional, with a biometric authentication needed in order to spend more than a designated 'default' limit by the wallet. It is possible in today's day and age. If they were able to create useless apps, I'm pretty sure they can create something important for people and enthusiasts too.