Regarding DomeLight requests - adding DomeLight would not resolve Corona's inability to store multiple environments for LightMix. That's a completely separate and more complex problem. What introduction of DomeLight would do is just making IBL setup in Corona more confusing and less straightforward.
Then there should be another solution for the cases when need to keep 2 and more different environments in one scene with easy access, control and switching. Not everyone works with the slate material editor to keep separate tab with different environment maps, so this is not the solution.
You don't need slate, you can have it in the compact material editor. For example create CoronaMultiMap, call it "Environments", and into each slot, add environment bitmap you want. Then when you need to switch them, just drag a new environment map and instance it into environment slot.
As far as complexity goes, it's about the same number of input actions:
DomeLight:
1, Select current DomeLight
2, Click checkbox to turn it off
3, Select another DomeLight
4, Click checkbox to turn it on
Environement slot:
1, Hit hotkey to open material editor
2, Hit hotkey to open environment window
3, Drag environment map from editor
4, Drop environment map onto environment slot
I am still wondering why do people keep requesting DomeLight. It does not add any new functionality, ease of use or speed. A practical example where DomeLight does something more or does it faster would be much appreciated.