While I think it's a great idea to provide more robust backup capability, with a large system like a cellular provider, I also have to wonder at what point things become economically counter-productive?
Don't worrk, the .gov will bail them out when that happens
Most sites already have some battery or generator back-up. Cost involved vs. revenue generated hasn't been that big of a problem for the telco's.
The C.O.'s, remote switches, and cell site shelters are not waterproof. Once they are under water (or even very humid) the electronics inside fail. You can supply all the power you want, but if nothing is on it won't take much.