A123 batteries are popular with RCers already. But they are bigger and heavier batteries so only appropriate for large planes or surface vehicles.
There are several variants of the LiFePO chemistry, the A123 being the most obvious example. They all suffer from rather lower terminal voltage than the normal LiPo ones, and all the ones I've seen have metal casings, so the do certainly have a lower energy density/weight ratio. That said, they're all pretty much bomb-proof as far as 'uncontrolled battery excursions' go, ie don't go bang if you do something silly to them.
However, they tend to be quite expensive, which seems to be the main reason that they're not used as much in RC planes. The weight isn't as much of an issue as you might think, as this type of battery tends to be used in quite large aircraft that can handle it easily.
Then can be charged at more than 1C rate though- something LiPos batteries can't do safely.
Most of the newer LiPo chemistry variants can be charged at considerably more than 1C now, some I've tried claim up to 5C, although 3C is more likely correct if you want decent cell life. The discharge rate is truly frightening, I have seen up to 35C continuously and 70C in bursts for some of the newest cells, which for example on a 5Ah battery could be over 350A
You can easily start a car with a battery you can put in your pocket.
They seem to have remarkably low internal resistance, so they don't even get warm at the rated discharge level. This could work against you, as if the things really did have a 10x current level of energy storage, you could get almost all of it out in a few seconds. They already have the energy density to potentially take your hand off, so...
pca