The only thing I can think of is that one of Courtois or Cech will be sold this summer with Buckland to become the no.2 behind him. Hilario and Turnbull will no doubt be released this summer as quite frankly, they are both awful.
I think it would be a bad move for him on a personal level as he would have little chance to command a place over either Cech or Courtois but money talks. I think you may trigger other clubs interest by making your bid also. I imagine should you sign him he will be loaned back for the remainder of the season till you get your glove wearers situation addressed.
The worst job at any club must be reserve goalkeeper.
I'd be extremely surprised if Cech left us. He seems very happy at Chelsea and I think his contract was recently extended into the far future. I'm not sure Courtois will ever play for us. He has done fabulously well at Atletico and seems to be happy there. Why would he leave Spain to be number two to Cech?
Maybe Butland should be number two to Cech for a while or be loaned out to some Premiership club. If we do buy him for £3.5m we'll very likely make a big profit out of him in a few years if he doesn't end up replacing Cech. It's a silly price.
I think both Turnbull and Hilario have been adequate reserve keepers. Hilario's getting on a bit. Perhaps he has a juicy bit of gossip about Roman he is keeping to himself.