Brian literally demoed it on his PC during the live stream to dispel these myths... and we've covered them a few times already in the last few pages of this thread.
Again as stated many times, this year's demo is actually much heavier than the one last year. Also if you do a bit of profiling on those stutters you'll find they are unrelated to IO and more related to editor and world partition stuff. They are also significantly less present in the cooked builds than play-in-editor or similar. Regardless, they are unrelated to Nanite.
There's no conspiracy here guys, I don't know why people *want* to believe it isn't possible when it clearly is.
For what it's worth I happen to agree with you that last year's demo looked nicer, but that's really just on the art. The two demos had very different goals.