This is a good call. It shows Wello is now very much a reserve in case of serious injury crisis.
More importantly, Wilkin is very much an aggressive in-your-face kind of player. Saints need that desperately since Graham left. He's clever enough to stay on the right side of controlled aggression, and he'll communicate that attitude to the rest of the pack when he's back where he belongs in the scrum. I don't see Roby as captain material, to be honest - he's not a big talker, and he needs to focus much more on his own game, playing as he does at hooker in the thick of the action all the time.
As for whether Wilkin deserves his place, I think he certainly does. We may have some good young lads coming up, but effectively they are interchangeable prop/2nd row types of the sort we've been producing for years - decent solid lumps who run hard and tackle lots, but don't offer a whole lot in terms of a passing game, organisational skills, or clever line running. I think the loose-forward position is made for Wilkin, with a slightly more old-school ball-handling, wide-running kind of role. The likes of Thompson, Savelio, Greenwood etc can take their turn rotating in the prop/2nd row spots and doing the hard graft. Wilkin still offers just a few more options in his game than they do at this time.