The number of users is almost irrelevant in the context of Nostr because many clients generate a new ID. These aren't email-verified/phone-verified users -- this is literally just a new key/ID being generated. Some web apps auto-create a new ID and join the network every time you use them. Also, the signal to noise ratio is really bad with a lot of spam and almost all discussions related in some way to crypto. Nostr…
Additionally, I tried a few clients, they were a bit buggy and far from anything anyone would take seriously for more than a minute. Key portability was broken on them as well for some reason I don't even want to invest my time investigating.
These decentralised solutions need to distance themselves from cryptocurrency (or at least make it in the background rather than the center of discussion and operations) to be taken seriously.
I see Radicle[1] did that by distancing the version control software from the cryptocurrency, and I think it was a good decision.