Well, mostly everyone heard of Xenu, for some value of "heard of", so I'm not sure what's your point.

So the poll would still be very useful for demonstrating that the Basilisk is a highly non-central and peripheral topic.

Yeah. So far, though, it is so highly non central and so peripheral that you can't even add a poll question about it.

edit:

(At this point, isn't it literally exactly one person, Eliezer?)

Roko, someone claimed to have had nightmares about it... who knows if they still believe, and whoever else believes? Scientology is far older (and far bigger), there been a lot of insider leaks which is where we know the juicy stuff from.

As for how many people believe in "Basilisk", given various "hint hint there's a much more valid version out there but I won't tell it to you" type statements and repeat objections along the lines of "that's not a fair description of the Basilisk, it makes a lot more sense than you make it out to be", it's a bit slippery with regards to what we mean by Basilisk.