What happens for leveling alts that are inbetween?

[majinbebi]

So I have several alts scattered currently in the 40-90 range, which I understand is going to be squished according to that fancy chart they recently posted. I also understand that you can level basically the entirety of your character in just one expansion with reasonable pacing.

But what happens to my alt who is level 70 who is squished to level 27? As an example, would I just start Wrath at level 27 and then finish early? Can I level in the expansion I already leveled in if I want to (lvl 70 char who hasn't been touched since BC leveling in BC again with friends)?

Have they posted anything that addresses this?

[Mirishka]

You pick your expansion of choice and work through it until you hit 50. Easy peasy.

[majinbebi]

You pick your expansion of choice and work through it until you hit 50. Easy peasy.

So I should pick the expansion with the early zones that I want since I presumably will only work through half of it (assuming leveling a lvl 70 char that is squished to 27)? Thanks, good to know.