Interesting question: what about them?
Right now I would agree with the 'case by case' approach as each case will be different. As mentioned already the specific type flown is a thing to consider. Can the aircraft somehow be saved when engines fail, or with elec/hydraulic failures? If the aircraft possesses a failure mode which could render it uncontrollable then a 'way out' is surely not too much to ask? (please note: I'd like to leave the question of whether such an aircraft should be flown out of this discussion)
Another issue though would be pilot proficiency. Pilots with military backgrounds will be more familiar with the risks and issues surrounding bangseats, as opposed to pilots who end up on a jet from a PPL/GA background. A pilot sitting in a bangseat should be intimitely familiar with the seat/aircraft envelope, giving him the option to evaluate when to use or not to use that yellow lever. Training for this would be needed!
And the third issue is of course how to maintain that seat. I think that stringent rules for this are a must and the task should be dealt with by a certified professional.
Just my two cents.