I get your point, maybe a loan move might work, but I suspect it would go the same way as the Lingard situation: he might have a superb few months, get the spark back, and then go back to his parent club and put his feet up for another year.
If playing football was truly the most important thing to Lingard, he could have forced the move / paid up his last year / demanded a transfer (I doubt United would have stood in his way). But he didn't. He was happy to pick up his big wages (perhaps more than WH would have paid him), sit on the bench and stay comfortable in his house and the cushy environment he's been used to for years.
I could see Deli Alli doing the exact same thing.