I'm affraid I've had no formal Krav training but have seen its syllabus and have a couple of books on it. I think Krav would be a great system for you.
I teach a guy who is also based in a wheelchair and he is an extrememly effective martial artist. Moreover striking, parrying, traping, locking and restraint skills are also essential for you to drill. I think Wing Chun also leads itself very well to Wheel Chair MA's, their method of power generation is very portable to the wheel chair.
Unfortunately, due to the small number of instructors experienced in teaching wheel chair users is limited, so it will require you to adapt a lot of the theory yourself. The Krav guys are reknowned for being sneaky and adapting to whatever needs they have, so I think it would be a very good system to look into. Perhaps JKD would be worth a look aswell.
If you want any advice on how we work please feel free to PM or email me at firstname.lastname@example.org.
I'm pretty sure Darren (our Wheel Chair user) would be happy to answer any queries you'd have. Drop me a mail and I'll try and put you in touch. Darren very kindly done a self defence bit on our website here
. The video isn't very smooth, its the first time Darren had done a demo, let alone a video...but it'll give you an idea!
Fighting from the chair gives you a very interesting perspective...I'd thoroughly recomemend that everyone tries it. Training with Darren has definately made me appreciate his condition and he's spirit to succeed despite his limitation is a sourse of great inspiration!
Hope that was of some help and good luck with whichever system you decide to pursue.