Where does the idea of Elanga at RB come from? Has it been mentioned by ETH or has he every played there?
It's my own opinion for a few reasons.
1. He perfectly suits the role of a modern fullback.
He works very hard, defensively trustworthy (hence why Rangnick kept him on the wing a lot over Rashford) and has blistering pace when running into space.
He's a decent crosser of the ball, can beat people if left 1v1 and has shown decent link up play. He's a goal threat too, which can never be a bad thing from a fullback. Aerially we've seen him chip in with a few headers now, I can forsee him arriving onto the back post and giving us more threat than AWB or Dalot.
Obviously he might need to work on his positioning and 1v1 defending, but AWB was a winger until only about 1 year before he made his Palace debut. If Elanga takes it seriously any intelligent player can play the role of a fullback. It's more about concentration than anything. There is also plenty of suspect fullbacks defensively who make up for it with being better going forward.
2. We will have a lot of competition on the wings.
From what I've seen of Elanga so far, although he's very young he is more about hard work and speed than skill and individual brilliance. Up against the likes of Rashford (if he gets himself together), Sancho, Amad, Antony (if we do sign him) and then we've got Garnacho breaking through, he might find himself a little down the pecking order.
I think Elanga fits a similar profile to Mazraoui who ETH loved, and unless he can work a miracle on AWB or Dalot, I think he will be looking for other options.
Elanga did play RB under Ole in one match for a period when we went hail mary and he looked good, but obviously that was an isolated situation so can't really be used as great evidence.
It's more of a gut feeling from experience, it might not happen, but lets just say it's something i'd keep an eye on.