Hi Neil, yes i understand your idea but if you do not have a desktop webstore what is the real benefit of entitlement?
Yes, you have a user management but you do not have a your real store!
Yes, you can entitle app users to specific content (single collection or subscription) and sure this is important!
What do you think?
NB1: And with entitlement you have anyway the cost of hosting (yes, only php+mysql hosting and without a https certificate).
NB2: the pay transaction fee of a webstore is very very less then Apple/Google/Microsoft fee. 30% is a number very impressive for every client!