I hate to poop all over your interests, but I just don't see a single practical purpose behind releasing new cassette tapes.
Just seems like a silly gimmick to me. I feel like any case for tapes can be made better for vinyl, digital, or CDs. I mean, if it's just for collecting purposes, why not just sell limited edition t-shirts, posters, and bobble heads?
Don't let my disdain for your hobby bum you out, though! I just don't get it.