I hope they add a "lock app" functionality witht he fingerprint lock. I might be ok handing my phone to a friend, but I don't need them going through my email etc. I actually had a cousin do that. Sat there for 10 minutes reading my texts before I noticed (thought he was gaming). I was so mad.
My guess is that apps like "app protector" ect will be able to utilize any of the security measures built into the phone just like they can with the pattern/passwords currently used. Here's to hoping.
On a side note, your cousin is not a trustworthy or good person if he thinks reading your texts like that is an ok thing to do. My guess is that is just one layer of his self absorbed personality. Least you know this now.