FWIW, there are gobs of people in The Netherlands with canes on their rear racks and a number with custom holders for their canes. I've never surveyed them to see what their various issues are, but invariably they'll get to their destination, use their bike for support, then grab their cane and head off. You'll also see a fair number with step-thru frames that drop below the bottom bracket. Whatever issues they have with walking do not seem to affect their ability to ride and many aren't exactly slow.