Hi,
I suggest a compromise. Now that we know you're branching the feature set. How about a one time only update of these new features back to the MVC5 versions? I'm not a far from releasing my first MVC5 app to production and would dearly like the subscription feature. I also have new projects coming and want to use ASP.NET zero for these but one requires ADFS so I'm forced to stay with MVC5 for now.
Also, i love this project. You're saving me a lot of development time.
Regards, Conor