Not the worst idea. I'd just be worried about how much more his body can realistically take. We've all seen how Horwill almost overnight went from starting week-in-week-out a couple of seasons ago to being a rolling "two-week" return from injury. It's a serious struggle for these guys in their mid-late thirties to keep their body in shape even to get through training each day, let alone play at high intensity for up to 80 mins each weekend, sometimes with a 5 day turnaround.
So it's a risk - 50/50 you could say. Either his body holds out for another year, or it crumbles. I'm sure AWJ already knows his next move - I personally wouldn't be surprised to see an announcement that he's retiring from all rugby after the World Cup and moving into a coaching role.
Sorry to be a killjoy.
Goes without saying I'd rather see a Snyman coming in (I'm sure we all would) but as that's looking increasingly unlikely I can totally see the logic of what you're suggesting and the risk could well be worth it.