Typically, the subscription model is for access to new or updated modules on the vendor's site for a given period.  I would check with DNNStuff for specifics

In my case, I offer a subscription for 3 periods: month, 3 months and a year. Any module downloaded during that period will remain functional "forever" based on the defined requirements.  If DNN implements any breaking change or Microsoft changes something, the module will evenually no longer work in that "new" world. 

For example, I had a version of SGSV for DNN V2, it will NOT work in the current versions as both DNN and Microsoft changed the underlying world.  If you have a DNN V2 site, then it will still work. 

Hope this helps
Paul.