I understand the appeal of a virtuoso encore, but lately I've been seeing so pretty famous pianists do relatively simple pieces as their encore, played beautifully, of course, things like a slow Scarlatti sonata, or Chopin's C# minor posthumous Nocturne or a Grieg air. If your programme is full of technically difficult stuff, the audience might actually like something simple and beautiful.
If you want a great Liszt transcription, Widmung is beautiful.