That would be totally super @Scottie!!
Don't get too excited! "That would require a fancy add-on" means that I would have to write one. As I mentioned earlier, I had to write an add-on to get old-style vid embeds to still work on the this forum. That took me the better part of a day, and it was VERY simple. Basically just a "find and replace" kind of thing. I'm still not sure how it works, because I patched together chunks of code I found on their support forum, and poof! It started working. That's
not how one writes software... but in this case, what else was I gonna do? IOW, it was a shot in the dark, and it worked, so I went with it.
The trouble is, there is literally zero documentation for how to write add-ons. The developers basically say, "Oh, just look through the code and figure it out!"
Well, okay, but... The source for XenForo 2 is basically layers upon layers of classes and functions calling other functions, ad nauseum. I don't really have that level of PHP programming ability. The old forum was written in the Old Stupid Way, which made it much easier to work with (for me, anyway).
So, the time investment required is off the charts for something like a Print Friendly view. It would require knowing how to access the database, get all posts for a thread, blah blah blah. In short, it would require a deep knowledge of the how the forum code works.
That's the bad news.
The good news is that since XenForo 2 is only about 5 months old, I'm hoping that as more and more people adopt it, they will rewrite their popular add-ons for this new version. And then not only will we have more add-ons to choose from, but I will have more good code examples to learn from in order to write my own add-ons.
As an interim quasi-solution, one of these days I'll probably figure out if I can add a "print.css" that styles a single page of a thread so that all the posts on the current page of the thread are viewable in Print Preview. That should be relatively easy to do. I'm actually surprised the XF people didn't worry about that, because it's pretty standard.