Let's make this a topic of its own.
As mentioned recently in the '[Idea] Allowing most keywords after "."'
thread, the 'default' keyword is only used as a keyword in switch
statements, where it's synonymous with 'case _:'.
It's also the kind of word which appears commonly in enums.
So, why do we need to keep it as a keyword?
Disadvantages: there would be some breaking of code, but a migration tool
should have little difficulty replacing 'default:' with 'case _:' in all
Alternatives: replace 'default' with 'else'.