The thing is no big team is in desperate need of a top keeper. PSG and Juve, maybe, but why would they want to shell out a huge sum in transfer fees and pay massive wages for a GK who was not in the best form for the past two years.
In addition, I think Sheff. will gladly take Dean on loan for another season. He will get to develop with constant play time in the top division, and we will probably see him in the Europa league, or maybe even CL with Sheff. and the club will be able to evaluate him based on a larger sample size.
By then, De Gea will have two more years on his contract, and things might look different. Who knows..
Look, I haven't been the biggest De Gea fan those last couple of seasons, but I think it's a huge risk moving him on just like this.
Come the summer, he might be the only truely WC player we have in our squad.