As BA allows 23kg bags as carry on (beyond me why they do that) I can see that many ppl who might have a problem lift such a bag into the overhead bin.
I personally would ask somebody to help me in that case (as doing it alone is quite risky, even though I'm young and fit). Even though in that situation I wouldn't be lifting my bag all on my own, I'm still perfectly capable of lifting an exit door if needed. But I don't think the bags are that heavy all the time and generally speaking if you can't lift your bag you can't lift an exit door (I think they were like 15kg?) and therefore shouldn't be seated there.
If the person is just too lazy to lift their bags and sits in the exit row, the rules above (who can't lift a bag can't lift the door) should be applied and they should be moved. (Instant Karma). If that was not done I would voice my concerns with teh FA.
As I usually fly Swiss I know that on those flights if you are seated in an exit row the FA will come by and ask you if you are aware and able to perform exit row duties.
I was once seated in an exit row some years ago and the FA came by to ask us exactly that finishing with the legendary sentence I will never forget:
With great leg room comes great responsibility!
PS: I really want to hear that CCR story!