Until the addition of the new scalar-unit.bitrate we had units that were case insensitive. E.g.: "hz" and "Hz" could both be accepted without ambiguity. But that's not the case with bitrate where "bps" != "Bps".
My suggestion is to clarify this in the spec. We can add this to section
"3.3.6.2 Additional requirements" saying something like "The unit is either case-sensitive or case-insensitive according to the concrete type", and then for each concrete type specify whether it's case-sensitive or not.
It might seem simpler to have everything be case sensitive, but I would argue against that, because people don't always know the correct case notation for various units. It would also break compatibility -- my impression is that existing 1.2 parsers ignore unit case.