One thing I discovered on my memorize-away-from-the-keyboard experiment is that I can look at a page of sheet music and hear it a lot better than I used to be able to. I am not to the level of looking at a score, atonal music, or music with a lot of accidentals and getting very far. Mozart and Beethoven (carefully chosen) are not too hard.
I’m starting with Beethoven’s variations in A on the song “Quant e piu bello l’amor contadino”. This is a fairly simple theme and the variations don’t look too formidable. I think I have the theme and 1st variation nailed. Next step is to try it blindfolded.