You won't notice it if you have a good follow/follower list and hang out there. Global was too chaotic to be useful before this, so nothing was lost to be honest anyway.
Only minor annoyance is notifications for me at least. But should be fixed soon.
User discoverability could be an issue in the near term, but this was a problem to be solved anyway and won't affect it too much.
Relay operators will probably prune spam messages from those npubs to reduce space on the hardware. In the future, they could always implement a optional blacklist similar to how the Yacy P2P search engine handles indexing of the web as a solution to this problem and just inform users of this.