After some good thinking and talk to our customers we finally upgraded to Unity 5. We still keep working also on Unreal Engine 4 to cover all our customer base, but we will keep all the development in parallel. This decision is based not just on the technology, because now, with IL2CPP, Unity and UE4 are par (well, Unity is better placed on the Web front), but mostly on the fact that the royalty based model in UE4 is not easy to sell to our clients 🙂
That said, we only upgraded the PC/Mac/Web license for now because anyway that's the place that carries the most of the new goodness in U5. In time we'll upgrade the remaining licenses.