If Blackman is indeed going (and I think we can stipulate to that), then Williamson wouldn't be a bad shout. He can play in that position and knows the turf, though of course it would be a regressive step.
We have gone from having tonnes of pace in the centre forward position to zero pace. We had Blackman, Cofie and Miller. Now we have immobile geriatrics (Cresswell and Kitson, though Kitson remains a useful player), immobile players in their prime (Porter), and in an attempt not to destroy the fragile confidence of young players, young strikers not blessed with alarming speed (Ironside, who seems to developing as more of a target man). Given this I wouldn't be against a quick striker, even though it seems like we have a kerjillion players in that position at the moment.
The centre midfield is a problem:
Doyle is awful but Wilson isn't going to drop the captain (why people criticized Bergen and I for pointing out the idiocy of extending his contract I cannot fathom).
McDonald seems to be in a situation where he requires handing with sensitivity so that he can produce his best.
Whitehouse, the obvious replacement, would ideally be brought in to replace Doyle. But if whoever is brought in is a central midfielder, we can forget about his development for another year. So in a way I hope they aren't.
A left winger would be a good idea.
All the above is based on the understanding that Foxy's information is correct, the obvious fact that selling Blackman is a terrible idea, and the absolute certainty that we are going to see little of Diego, much as we would like.
Fundamentally it's difficult to get excited about the (putative) arrival of new players when the squad as a whole lack cohesion, effort, fluidity and determination. It is this that needs to be addressed, and it isn't something that a couple of new faces can affect.