I like stealth games as much as the next person I suppose, but a truly invisible person. That would be a bit much. Plus, a lot of modern cameras (especially for high-end government facilities) already have thermal cameras at least in some of the rooms. Thermal sensor arrays, motions sensors, and the like. The problem with stealth in games is that it requires an obscene amount of finesse (which might not all lie on the gamer to provide, but the developer) but more than that stealth is very passive. People tend not to like passive anything in general. Obviously, there are exceptions.
This is why I like Splinter Cell: Conviction. Everyone said, "That's not stealth! You can hardly sneak by anyone and them not know you're there!" Well, it's not sneaking stealth I grant you that. Here me out. It's dynamic stealth. This is something not a lot of people do. Conviction wasn't about getting by like a ghost. It was about being the specter of death. They're all going to die and they don't even know what hits them. They're two sides of the same school, and any good stealth game will incorporate levels of both.
Still, I see your game having this kind of dynamic potential. Sure, there's a lot room for the more traditional fly-on-the-wall kind, but what about having to move across traffic? You have to do it quickly (something the average stealth player doesn't like. You couldn't most likely use a cross walk for fear of alerting a pedestrian, so you have to go around the cars as they inch forward in gridlock traffic. You couldn't go behind them because the exhaust going around your body would be an obvious tell to anyone looking.
If it's not obvious I spend a lot of time thinking about immersion. I don't like that you can't see your feet in a lot of first person situations, so to speak. I call for more dynamics in games in general, because let's face it. Even your best stealth games reduce things down to some pretty standard formulas. I don't know if it's ever entirely avoidable, it's probably not. I think Dynamic Gameplay would go a long way though.