Just FYI: https://www.rfc-editor.org/rfc/rfc7999.txt
I guess this feature deserves to be implemented.

Oh, sure. We plan to implement it.

It would be nice if export filters for the Kernel protocol could set a route type, as in iproute(8):

TYPE := [ unicast | local | broadcast | multicast | throw |
unreachable | prohibit | blackhole | nat ]

That would probably make more versatile than a static RFC7999 hack, while allowing to easily implement RFC7999 and others.

Greetings,

Clemens