To quote myself from two posts above:
60 is the new 50. Literally. New players will skip Shadowlands completely and just level from 10 to 60 in BFA and then go to Dragon isles.
So leveling from 1 to 60 in Dragonflight should take as much time as leveling from 1 to 50 does now. Which it will, since currently you need 2163990 XP to level from 1 to 50, and in Dragonflight you will need 2091800 XP to level from 1 to 60. It is slightly less, but not by much.