Bingowings said:

I think Yoda suspects Anakin might still be the wild card.

He should have been "The Other" instead of Leia after ROTJ turned out to be the last film ever.

Almost everyone other than Luke seems to have forgotten that Jedi.

I agree on that. I once suggested this on IMDb boards but people didn't like it. :)

Actually I went a bit further. Maybe the main plan of Obi-Wan and Yoda was to just use Luke to trigger the return of Anakin. I think it is a bit too much to hope for that Luke could defeat both Emperor and Vader, especially when they started to train him at the age of 18.