Something along the lines of
api.tvmaze.com/user/followed/shows?token=XX... (or whatever URL makes sense to you guys)
Using the same token as the ical feature and returning a simple JSON list of the shows the user with that token follows.
This can be just the show IDs as far as I'm concerned. Alternatively, it could use the same type of output as the search shows API (api.tvmaze.com/search/shows?=).