Fugliness
Solving problems that we don't notice while creating problems which we do notice doesn't seem like it's going to help us massively. I think there's still quite a lot that would need to improve before this could be used on wider scale, like the mess it makes of recent changes, user contributions & watchlists by having edits & comments in conflicting formats.
I'm still not convinced that this will be an ideal system for wiki-noobs. Most online forums have a straightforward system where users either reply to an existing thread or start a new one, but liquidthreads is more complicated. Being able to cut & move threads may be useful, but the reply button against each individual post is confusing. It's not obvious whether the right thing to do when posting in a thread is to reply to the initial post, or reply to the post above. Plus there's always the possibility that a new user, who is used to wikis but confused by liquidthreads, may just click "edit" at the top of the page & hence start a thread outside of the liquidthread & make a mess of the talk page.
I guess the best way to check whether it really is user-friendly for noobs would be to post welcome messages etc. using liquidthreads on new users' talk pages & if they respond to it. But it's probably a bit early to try this yet.
tl;dr version: There is no ideal way of communicating on the internet.
By "not noticing" problems, I suppose should have said "problems we don't care about and just begrudgingly accept". Don't tell me you like edit conflicts! :P
Some forum systems do have reply buttons to individual posts and thread the comments in a tree like structure. I will grant you that those aren't as popular anymore as the linear ones (and seem mostly restricted to old-skool newsgroups), but the alternative to specific replies like this is to go completely linear then add the quote box option as done in other forum systems - so you quote and then add your response and this sort of thing is built in. This method is nice and all but it's a bigger deviation from the usual wiki-way, and anyone who's seen a dozen nested quote boxes will know how bad that can get if it's not controlled! I think this system is an good compromise between the usual wiki-way of doing things and a more flexible and powerful forum system. It's certainly far more compact than a lot of other ones where 90% of the screen is taken up with sigs and avatars and post counts and quote boxes and loads of extra buttons about things. Once you've spent some time in phpBB or SMF or whatever (this is what I am/was used to in my pre-RW days), you find that LQT is a minimalist breath of fresh air.
I see your point about those used to wikis getting confused, and indeed I think people might if they're used to editing. But the way of doing it by wiki is something you need to get used to and learn anyway - it's a complicated piece of etiquette that was designed out of a system not meant for discussing things and as such is not an ideal solution. The talk pages are meant for brief comments regarding articles, where things are focused, to the point, and likely to get one edit every few hours, if not less. So in the case of RW where we may have faster paced discussions where people with larger entries (an entry this large would certainly get an EC in the Saloon Bar, I'd wager) there are areas where LQT would be beneficial and removes the farcical aspects of the wiki-way. "Retraining" back to threaded comments can't be too hard comparing to learning the system in the first place.
I also don't think the etiquette of what comment you reply to is anywhere near as complex as the manual indentations of the existing wiki-way (in big discussions, this is borderline farcical). Here you simply reply to the thread you're responding to; talk to the OP, reply to them, talk to the last commenter (as I'm doing now) reply there, talk to a person above specifically and go there. Excessive nesting may be a problem, but that's a problem anyway, hence the "undent" trope. This is something that can hopefully be fixed in LQT and perhaps added automatically, again this would be solving a problem we begrudgingly accept. I think that's considerably more intuitive for branching discussions compared to the usual wiki-way, where it feels like you're actively discouraged from replying to an earlier comment (or need to add a lot of exposition in to explain yourself). You get a new message either way, so it will be read by those in the thread.
With clicking "edit", that can be switched off to make it n00b proof, as I believe it is on Nx's talk page. Similarly, such an edit button isn't visible when responding via the "new messages" page.
I'd be against adding LQT to new users pages, but I can see that would be an interesting experiment to try if they opt in. It be interesting to see someone with no experience of wiki-way etiquette use it - I honestly think it won't be a problem.
