This is a great idea.
They could possibly get around the Hook-as-leg issue by having dual-purpose pegs at either end that would work to both stabilise the shoulders and form a leg...it'd be tricky and probably out of budget but I imagine if they played with chest width and leg length a little then HTT could engineer a Hook mould that could be either a foot or an upper chest.
Of course, that would mean people wanting an IDW-accurate Prowlastator would need to buy 2 Hooks, but I doubt Hasbro would mind that all that much.