There are only two cases where that's been a thing. Macros, and nonlexical lifetimes.
The major rewrite for macros has already brought fruit with Macros 1.1, solving some of the more pressing issues.
The other one, nonlexical lifetimes, needed a complete overhaul of compiler internals. The main part of that work happened with MIR, but there's still work to be done. It's ongoing. This was work that was going to take a long time, and it did.
I mean, it would still have taken time. Should they have delayed 1.0 and stability for it? I don't see the benefit.
There have been plenty of quality of life features that were promised and delivered successfully. Many new ones have been discovered and are in active, visible progress, but are not implemented yet, so yes, you can always identify some pieces that are still being developed. The amount of resources is finite, but Rust is getting significantly better each year.
What else is that a response to? Macros have had this planned since before 1.0, with the current system specifically designed as a temporary workaround until it that happens.
I agree, the macro scoping is just a small part of the rewrite but it is a problem (especially ergonomically) that rust should have got right the first time around.
Right now macros don't quite feel like they are part of the core language, but instead a hack or plugin slapped haphazardly on top of the compiler.
The major rewrite for macros has already brought fruit with Macros 1.1, solving some of the more pressing issues.
The other one, nonlexical lifetimes, needed a complete overhaul of compiler internals. The main part of that work happened with MIR, but there's still work to be done. It's ongoing. This was work that was going to take a long time, and it did.