Hi,
I was working on a new feature this week end which is near what you are proposing.
My idea is to have a (or several) Joomla group(s) attached to a vendor.
A group will give rights (ACL) and specific permissions (changing limitations, like the product limitation).
Thanks to it, we can imagine that we can plug the subscription system with a plugin which will assign groups to the vendor who buy it.
So we can imagine thanks to it that we can have a dynamic ACL system using HikaShop products to unlock features or change limitations.
Could this feet to your requirements ?
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.