I sense this is a client GUI question. If someone want to begin doing nich relays they also need to built a client adapted for that environment. Atm. most client deal with all relays as if they where general relays.

A nich relay world would cooperate better with clients that has gui for specifying where you do your notes posting. Say that you where given tabs that post to different relays. So my "Food tab" posts to food niche relays, and "Photography" post to Photo niche relays.