> That said, it seems easy to make this backwards compatible: if the existing #blah syntax is a valid link, that should take precedence.
That's indeed how it works. The majority of the compatibility concerns appear to be with apps that a using _custom_ parsing of the fragment to perform app-specific logic, which is a valid concern.
That's indeed how it works. The majority of the compatibility concerns appear to be with apps that a using _custom_ parsing of the fragment to perform app-specific logic, which is a valid concern.