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