The Unity and Unreal models aren't open source, so if you want open source as a feature, as well as revenue, you can't quite copy their models.

To get open source together with revenue, you'd need to use one of the open source business model approaches.

One of those models is "open core" where the core product is open source, and there are additional features for pay which aren't.

Another model is to use GPL or a similar copyleft license for free, and require a license fee for a more open license. Qt is a well known product that uses this (qt.io), and they also offer a revenue-based discount so that smaller businesses can pay less.