I mean, I absolutely do not want one from Facebook, or anything else from Zuck, but even if a company not founded on advertising revenue offered one I don't know why I'd want it.
It's surely a popular use case, but I don't think it's going to be enough for it to spur adoption the way it allegedly did for VHS / home video. There are a couple of big issues with it.
The biggest right now is probably lack of standardization in terms of video quality and features. It's difficult to find any VR content that maximizes the capability of even the Quest 2, much less porn. There's lots of stuff out there that's listed as "8K" and such, but is actually either badly upsampled lower-resolution video, or has been compressed so much by the streaming provider as to be unrecognizable. Likewise, most outlets tag content as "VR" but don't distinguish between 2D content that's been "split" into two video streams, 2D SBS (side-by-side), 3D SBS, etc. This isn't an insurmountable issue; at some point we'll likely see headsets become popular enough that it will be profitable for a company to move into the space and offer consistently high-quality content.
The other issue is hardware-related: the apparent pixel density just isn't high enough yet for comfortable use long-term. I like my Quest 2. It's the first headset I've had that doesn't suffer from bad "screen door". The resolution is still too low to use it effectively for anything text-based, which is a shame because I really want to use it to interact with a virtual desktop for terminal-based development work.
On the same token, you have people that will drop thousands of $$ on cam girls, none of whom are camming in VR.
People will pay for porn, just not the type that was thought up in a brainstorming session by a bunch of computer vision nerds.