I use Zwift almost exclusively for Workouts. What would be great is to select a workout I have previously completed, and be able to see the ‘ghost me’ (my previous workout) and to ‘compete’ against this. A modification to this would be to add an offset (% or actual Watt offset + or -) depending on whether you were aiming to make the workout harder or easier.
There already is a Feature Request quite like yours: https://support.zwift.com/hc/en-us/community/posts/203317699-Personal-Best-Bot?page=1#community_comment_206524596
(and I would love this feature!)