I think good fill in for Delly's PG duties is a better to description of what he is doing currently. I think at this moment we have alot of guard that fall into the category of being your 3rd best guard in rotation. In different team constructions, Delly, Knight, Nwaba, or Clarkson could be a teams 3rd best guard. I don't think you would want any of them to be your 2nd best guard when fully healthy.
I think Knight could be a teams 3rd best guard that gets heavy minutes and if he has to play as your second best guard for stretches, it wouldn't be bad. I'm not sure anyone else on our team falls into that category.
That being said I just don't think we need him long term. We will try to find someone else to pair with Sexton for our starting backcourt. I would be happy with Delly and Nwaba as the guards that rotate in, in the near future. Also the league has move from combo guards at SG to wings. You would think we would want to go to a wing heavy roster vs a guard heavy.
Pair all that with Knight's injury history and I would move on from him in the summer or at the trade deadline if we got a 1st round pick for him. I actually think a contender would see a healthy Knight as a better fit than Clarkson.