The problem is that many/most newer laptops have touch screens. ISTM, it’s not that the previews are enabled for mouse-based devices, it’s that they’re disabled for touch screen devices (which would include tablets and phones).
What would happen if that feature was turned off? Will something go wrong if previews are enabled on a touch screen (without a mouse) device, like a phone? Since you can’t really hover on a device with no traditional mouse, I’d think it wouldn’t make a difference.
Not Apple devices 
About all you can do on touch as far as emulating mouse hover is touch-and-hold but that’s usually for a contexual menu like “open in background” or “share link” etc, which is right clicking equivalent, not really hover. There’s really no equivalent for “hover my finger above the screen”, though I think Samsung experimented with this.
That’s basically what I’m saying. If preview were enabled for ALL devices, would it make a difference for a mouseless touch only device? That is, if you didn’t disable preview on touch screen devices, then I could hover over thread title with my laptop (which also has a touch screen), and see the preview. On a phone or tablet, with preview enabled, it shouldn’t make a difference, since you can’t hover on those devices. Would doing that create some other problems?
Aha, I found the Samsung experiment
I thought of something while I was making that last post. Turns out if I disable my touchscreen, which I use almost never, the preview feature works fine.
Yeah, I’m not going to break my computer’s functionality for one website.
It’s too bad, though, because as it is, it’s confusing and inconsistent for a fairly large fraction of users – pretty much anyone who uses a new PC and either an older PC or a Mac. And I’d guess that’s a decent fraction of the population, since many people have their own device but also use an employer’s device.
Although, I hope you don’t decide to make it consistent by killing the feature, which is a really nice feature. I mean, you probably should, if you can’t fix it, because inconsistent behavior like that is extremely frustrating for users – more frustrating than not having a feature you might never have thought of. But now that I’ve worked out what’s going on, I selfishly hope you don’t do that. 
Of course, best if you can actually fix it so it works on any device with a non-screen pointing device.
I normally wouldn’t either, but I really don’t ever use the touch screen. In fact, I’d been meaning to turn it off for a while since, more times than I can count, I’ve accidentally closed my browser by bumping the screen while I move the laptop around.
Hey, I appreciate that you have been helpful here, posting in threads to help us understand features or know how settings can be adjusted. And it’s great when there are settings that can be adjusted, even if the board owners haven’t adjusted them.
But it was you who pointed out you could change the software, so I was asking if you actually had. Fair enough if the answer is there is no need to because the software already has the suggested change as a setting.
It’s really up to the browser engineers (Chrome, Firefox, Edge, etc). We need a way to distinguish, in JavaScript, between
Right now we are missing that one in the middle.
Do you need the middle one? Can’t you do something along the lines of:
If touchscreen only device
then don’t allow mouseover previews
else allow mouseover previews
But I’m still not clear on why it can’t just always be turned on for all users all the time, regardless of the device they’re using. If they’re using a touchscreen only device, they simply wouldn’t have access to that feature. Everyone else would. Unless, of course, it causes other issues.
To complicate all this, I think it’s safe to assume that the the line between mobile device and computer is going to keep getting blurrier. Who woulda thought that someday we’d be at the point where just about the only thing that separates a phone from pretty much anything else with a screen is a SIM card and there’s certainly ways to make calls without even that.
Why do you care if a device is mouse-only? What if I have both a mouse and a touchpad? What if I have a touchpad and a touchscreen?
Honestly, I’d have the preview work except in mobile mode. I don’t know what mode people with tablets usually use, but what would be the harm of having it enabled on a tablet?
Welp, that stopped working after a few days. I don’t think anything changed on my end, but as of today, I no longer have previews.
Not that it really changes your question, but I assume a touchpad counts as a mouse/pointing device.