Life or lithium ion will be the next battery technology.
I just dont much care for the Lipo era. A123's are good cells too.
A123 batteries are used in hospitals. Now they are for RC.
A123 have been out for a while, while Life is just getting started.
It's just impossible to make a life or A123 into a saddle pack
without modifying your chassis.
That's why Ive stayed with high capacity nimh for now.
I run 5000 elite nimh packs in my 501x. Have good punch and lifespan.
I keep up with the Lipo guys fairly easy.
After all it all comes down to the driver, not the pack your running.