This looks great indeed - I wonder if there are any particular gotchas, though, as things often are in C++next land.
With many of the features coming into the language over time, I kinda wish that a bit more restricted subset of it eventually becomes a thing, but I know in practice it might as well be a completely different language. That, and I expect that still many other things have not been resolved as well as they are elsewhere, such as build system and dependency management (although I haven't touched this stack for a while now, so I would love to be surprised).
"Holds a value, except sometimes"
The gotcha is that this is a 90s C pattern, and software that actually needed this has been written for 3 decades by now