While I like your line of thinking, I see some problems with your idea. Like you said, RPGs are one of the biggest threats to lightly armored vehicles, especially in an urban setting. Basically, an RPG is little more than a highly improved bazooka. It's unguided, so it's jamproof and cheap. They only cost a few dollars each. In addition, RPGs have a short effective range, so the flight times are very brief. In an urban setting, someone can fire an RPG from a rooftop or alleyway at ranges so short that the flight time is under a second.

While a radar or IR technology can detect the launch point, you wouldn't have time to slew a weapon and return fire before the RPG hits you and/or the shooter has a chance to move. Further, the shooters often work together firing their RPGs in huge numbers. I've read that in the "Blackhawk Down" incident, dozens of RPGs were fired at the helicopters who were unable to dodge them all.

In the case of a vehicle like the Stryker, you might detect and try to engage one shooter only to have a dozen or more others shoot you in the meantime. This would almost certainly overload any automatic counterfire system. Your AEGIS example doesn't really stand up for ground vehicles. AEGIS uses multiface phased array radars and dozens of missiles to stop incoming aircraft or cruise missiles. They do carry Phalenax (sp) cannon systems as a last resort, but that just doesn't compare to the challenges of fitting the necessary computer, sensor, and firepower into a vehicle the size of the Stryker. You'd need the equavalent of the AEGIS missile system, perhaps mounting laser target designators and short range guided missiles on the outside of the vehicle. The vertical launch system of the AEGIS probably wouldn't be available due to ballistics considerations unless you could develop something that could launch straight up, veer to the appropriate direction, and then engage the shooter with a submunition. Parts of such a system have already been developed but not for that purpose.

For the foreseeable future, I suspect the best countermeasure will be improved armor and tactics. Low velocity shaped charge weapons like the RPG can be defeated with better armor technology, but that comes at the expense of weight. One of the reasons why LAVs are being put into the inventory is that heavily armed vehicles like the M1 Abrams are so heavy, they're hard to transport to the battle area. Improved tactics can help reduce the vulnerability to RPG attacks, but they're hard to implement in an urban environment.