I don't think the weight penalty of impact protection systems, and the financial penalty in terms of getting a new system trialled and approved, and the on cost, would prove to be worthwhile.
Crash protection is not really about weight. Take Formula 1. The cars became faster lighter and the crash protection amazing with modern formula 1 technology.
Cirrus are dipping their toes in the right direction I would like other manufacturers to follow suit and to make aircraft which protect pilots from themselves.
Pace