I love Walt, but coaching is so much different from playing the game. This man had more talent than our entire roster of OL combined - its hard to coach up talent thats just not there. That said, I'd love to have him on the staff in some capacity.
But what I really want to see is Tom Cable coach up actual offensive linemen for a change. Not converts from mid school. Not former tight ends and defensive tackles. Not a center the same size as our vertically challenged quarterback. Not random stiffs from another practice squad. ACTUAL offensive linemen.
If our line still stinks with that, then Cable is the root of the problem and should be let go. And maybe then you entertain the idea of promoting Walt to OL coach. Aside from that, I really think this is a personnel issue more than Tom Cable not being able to coach.