Sup.
I've been considering this a lot (see: just made a thread about the tulpa zine.)
I don't really have an opinion of the mainstreaming of it. If it happens, it happens, and there will be consequences for everyone, positive and negative. It's inevitable if this occurs, and I think the response shouldn't be "no, that can't happen" or "how can we stop it". I think it becomes an issue of getting shit together and presenting as a community of which the mainstream can communicate with, without coming off as crazies, teenagers, or pretenders. A pre-emptive strike of sorts.
Personally, as someone without a tulpa, I have tried to have conversations about tulpa to multiple people.
A few of them, surprisingly, would recount how they relate to tulpa. For example, an imaginary friend, rogue voices, etc. They all have the sentiment that they thought it was schizophrenic, unusual, and shameful. There seems to be an outstanding paradigm that the human mind does NOT hallucinate on its own (e.g. without drugs); if it does, you're sick.
The rest of those that responded to me prove this point: normally mouth agape, eyes wide, and the more I talk, it seems the less credible I become. They thought I was crazy, and this is coming from someone who does NOT have a tulpa. I can't imagine trying to communicate the idea as a host.
For tulpas to become acceptable in the mainstream, the mainstream has to accept the fact that hallucinations=/=drugs and schizophrenia. I think that when people talk about meditating, etc. as well, it is automatically connotative as being meta and not having real-world effects.
Back to my zine, this is sort of what I want the purpose to be. Something devoid of memes, tropes, and presented as a professional looking publication with production value. It's bells and whistles, but those are what legitimize information more often than not before scientific academia will take a look at it.