I seriously doubt it will happen at all, but if it does, it will be in the dual. Lee won't move up for the season to try to beat RBY to win the NCAA's. That would be foolish, but depending on how the season is looking, there may be motivation to do it for the dual. I think Ayala can wrestle a dual or two now and still keep his shirt in tact, right? If Iowa thinks they need a hail mary to beat PSU and having Ayala-Lee try to sweep Robbie-RBY instead of a guaranteed split of the weights with Lee at 125 and RBY at 133, then they may just do it.
That would easily be the match of the year to watch. My heart wants RBY but my brain says Lee would have a small advantage. It would depend on whether Lee could get a quick takedown and build a little lead early. If the first ends 0-0, the advantage swings back to RBY later in the match, but Lee's first minute is probably the best I've ever seen.