Exactly!
Ashley Young is half the player Nani is and 2 years older.
I don't think Young is a better player from Nani, but i could see that transfer-around happening.
I could see United bringing in Sneijder, as the first 11 replacement for Giggs at CM. Doing that means, imo, Park as first choice left winger in order to add a bit more defensive solidity as he did in the Chelsea games beside Giggs for example. If Nani doesn't push Valencia from the first choice right wing spot then he would be pretty much demoted to a second choice player. In those circumstances, I could see United selling Nani for a good sum of money (27million quoted for Juve/Inter transfer battle) and bringing in Young as a second choice winger on either flank for possible half of what we sold Nani for.
It wouldn't be a terrible bit of business imo. Possibility of using Nani as bait to get Sneijder, or if we were to move for Modric just use proceeds from Nani sale to fund the move.
I have previously read that Nani is very much interested in playing in Italy, so that is another part of the story.
Again, I don't think Young is a step up on Nani, but I think he is perhaps a more realistic 2nd choice winger, and he wouldn't be a bad one at all imo.