I don't think this is a good idea.
If someone wants to be updated about your work, there's already plenty of ways to do it. The follow feature is one of them. I don't see how "this is itch.io's building their relationship with their costumers, not me" makes sense. Your followers follow you for news about you and get notified about your work.
What I understand is that you want a direct way to contact people who tried, but didn't like your work enough to follow you (or subscribe to your mailing list, discord, etc.), which is absurd. Downloading something does not mean you will like, care or support it. Most of the games I download on itch I get just to see if I'll like them. Giving away my private information is absolutely not a commitment I'm willing to make just to try something out.
I get that demanding feedback instead of money sounds great, but I don't see how it could be enforceable. I think the best you can do is ask nicely.