I was curious to see if a batik style dyeing could be employed for wool felt, here I have used liquid cold wax on a piece of rainbow dyed prefelt. I think you can see from the photo that the wax had a tendency to sit on the top of the wool so I tried to push it down using the nozzle on the bottle. Hot wax might work better.
I used some black and magenta dyes over the batik and steamed for an hour. As you can see the wax has melted and spread across the wool.
This is the reverse side, no wax is visible and the dyes don't appear to have been hindered from penetrating the wool.
This is what it looked like after removing the wax with a hot iron. Although the lines aren't as distinct as what you get with cotton, I was surprised to see any lines at all given how the wax wanted to sit on the surface of the felt.
It sort of worked but gives quite a delicate effect.