The current situation is a little bit confusing. if I’m working with EEVEE, and I try to use the Nishita sky texture, no one tells me its not supported. I’m just seeing that its not working. so I need to google it and figure it out all by myself.
I think any feature that not supported by the selected engine should by hidden by default. this is the first step.
the second step is to make a dialog when you switch between engines that tells you what feature can’t be used and if available, offer you some default fallback. (like in the sky texture situation, you can use the other options.)
(I love the idea of the two engines using the same features exactly, which allows to switch between them without any impact on the render, besides render quality and render time.
but the current situation is far from that. and a little bit confusing.)