I can't remember if I mentioned this before, but... I've been assuming that the power levels would have to be adjusted a bit for a story like this to work. I just sort of took that as a given, but apparently it's not.

I.e. If you are going to insert super-humans (Narutoverse Ninja) into Middle Earth, which is comprised of carious non-super-beings along with a handful of BAMFs who mostly stay out of things, you need to bump up the Middle Earth baddies.

You could just do it without saying anything, but you could also handwave it and mix in the explanation with how Gandalf ended up in the Elemental Nations. Sauran/Saruman/Someone managed to access some Chakra and started pumping it into the Orcs/whatever-else, and now they're a bit more badass than the ones seen in LotR. Gandalf sought out the source of this mysterious energy and ended up in Konoha.

Or whatever. But meshing the worlds a bit more and adjusting power levels to prevent a curbstomp is fairly common in fanfic.

You can do it without that (and a few people have suggested ways to go about it), but it has its own issues (also mentioned in depth in this thread).

I'll go on record as preferring a pre-timeskip Naruto though. Hell it'd be fun to even make this cover some of the time period during the timeskip. Have him go off on this quest instead of off with Jiraiya. Maybe he can start to learn new techniques to keep things fresh while he's in Middle Earth, and so on.

My point is that there's loads of potential here and a few ways to bring it out. The thread just seems to be getting caught up in the minutae of power levels and whatnot. It's important, sure, but story trumps it in my opinion. Write a good enough story and people will read it and deal with some suspension-of-power-level-disbelief.