Hi Dimitrov,
Great suggestions. Thank you.
Unfortunately we cannot provide legal advice to licensees.
Handling all this with additional functionality on our website is interesting but it will take time to consider, prioritize, develop, test, etc., etc.
In the near term the simplest and most straightforward was to handle this might be for the developer (you in this case) to make sure the buyer and ultimate commercializer of the UE4 game is a UE4:Subscription licensee and is aware of the royalty obligations that go with it.
Best,
-j