The only issue with bringing him up is that you’re then stuck with 7 WR’s on the roster as none of them would clear waivers and make it to the PS. I personally don’t see a huge issue with that, but 7 WR’s on the 53 is a lot based on what teams usually do.
The other thing is, the only WR that hasn’t contributed is Foster, so you have to decide whose a bigger weapon for the 5 snaps a game they’ll get, Foster or Williams. This is made more difficult by Roberts being health and active now.
Personally, I prefer to sit on Williams until an injury frees up a spot for him.