I haven’t particularly tried to add an indicator of the time left in the loading process, but I’m under the impression it can be done in C++, but I haven’t tried it.
With this at least the level can unload into an empty level and show that it’s loading since one level must always be cached before it can be unloaded. If you have a fully developed level and tried to just transition straight into another fully developed level, some lower spec PC’s can’t handle the load and could crash out of memory.
Everything locks out when it’s actually loading so I think that the only way to retrieve that progress and display it can be done in C++. I could be wrong on that.