I am wholly against removing it, the main problem of NN is certain worlds having power-hungry mentors ruining it. The simple solution to that would be to allow players to report people for this and have them lose the Mentor status permanently.

also, a true global chat simply would not work
i don't know about other worlds but on Excal theres a common agreement among most people that advertising and spam isn't allowed in NN, a global chat without constant moderation would just devolve into RP adverts.
And at peak hours there are likely thousands of players online on any given world, a chat with that many participants would be far too fast to hold any real conversations, NNs requirements (easy as they may be to complete) and player limit of 100 mentors and 412 sprouts keeps it at a reasonable pace.