It would be nice to see various spaces characters (EM, 1/6, hair [non-breaking] space) to be provided by LO if they are missing from the font itself.
Most fonts do not include them while they are important for creating professionally looking documents.
Adding needsUXEval because I can't image how this can be done.
Although I support the idea of having better support of different space characters (if they are part of a font or not), as different space characters are really important for professional writing as the bug opener said. This also includes easier handling of space characters e.g. for space between digit and currency or digit and units and so on.
This is already implemented. HarfBuzz will emulate various spaces when not supported by the font.