I don't have any proof and if I knew where to get it I would supply it, but reddit's porn scene is huge. There are almost 5m people just on /r/gonewild
If the "Map of Reddit" project is any indicator the total NSFW subs are about one-third to one-fourth the size of the total non-NSFW subs. That's a non-trivial amount of use to gamble with, but the legal and regulatory headaches may make it necessary.
It may even be higher than that, because some of the usage of the other subreddits may be a consequence of being co-tenant neighbors to the NSFW subreddits, making it easy to move between the two kinds of content on the same site.
Which as a url, doesn't necessarily trigger corporate or school blocks unless the gateway is whack-a-mole filtering on subreddit names as well, and I suspect quite a few of those are designed not to reveal the nature of the content through the name alone.
Map is generated by clustering subreddits based on users who comment across subreddits, so I don't think you can infer much from the colored area. That's just background for each group of the graph.
I’m not saying it’s small. I’m sayin most of it is easily replaceable content-wise. My hypothesis is that NSFW communities (what’s hard to replace) are a relative small fraction of all NSFW subs.
https://anvaka.github.io/map-of-reddit/?x=18239&y=12514&z=46...