As someone who walks with a cane, I can partly answer the mobility part of the question. I use it because I have a drop foot, meaning a lack of control in my ankle. This doesn't affect me in the slightest on a level surface, and I would be perfectly capable of helping people out of the aircraft. My problem would be getting away once it was my turn on the ground; I'd be likely to fall flat on my face before five steps if we weren't on actual pavement (as I proved in a non-emergency once in a dirt-and-grass parking lot).

As far as the cane being an impediment goes, mine would be in the overhead bin so no problem for others (except the yahoos who insist on taking their bags with them).