Oh yeah, nothing makes a mess of your network like someone coming in and saying "we need to remove these IPs from the middle of our advertised blocks for security reasons".

I think we're going to see less of this due to IPv6's design, renumbering is less of a pain than it was with IPv4 so instead of splitting off a route in the middle of your address space and bloating the BGP table you can just move to a different subnet entirely.

Network Operators dislike buying new hardware. As the policies matriculate through tiers of providers, raw numbers of announced prefixes becomes a sticking point.