3.0 is an expansion of 2.0. It's not an issue of scrapping the entire game and starting from scratch with an entirely new game like was done when 1.0 was shutdown to be re-launched as its sequel, and that's essentially what people are suggesting when they talk about new characters starting at or near the (current) end so they go straight into the expansion content.
What we could see (and in fact, I'm really hoping we'll see) is for it to include some lower level side content added that could be done in parallel with the main storyline, hopefully with some long enough quest chains to develop meaningful side-stories.
That could let current players starting over from scratch with new characters feel they're getting to some of the new expansion content early on (though of course that's irrelevant to actual new players, since it's all new content to them regardless of whether it was introduced in 2.0, in any of the 2.xx patches, or in 3.0).
It would also allow players going back to advance additional classes some more story-based leveling content, which is an area currently lacking in the game. (ARR has a good story in the main scenario, but that's done with your first class, whereas all other classes get stuck mainly with just grinding to level up. Having more meaningful, story-telling sidequest chains could really help make leveling additional classes feel like it's a real part of the game.)
But even if the expansion includes a number of side-story quest chains at various levels, the main bulk of it is going to be in the 50-60 range and come after the existing main scenario. If starting from scratch, then you go through the whole 2.0/2.xx storyline which then leads into what happens next in 3.0.