Elixir of Ancient Knowledge, Elixir of the Rapid Mind, and Excess Potion of Accelerated Learning will become Poor quality and no longer usable. The Draught of Ten Lands will still retain the 10% experience bonus but will now be capped at level 50.
Why not convert all of the Elixirs into The Draught of Ten Lands so you don’t cause people to loose out on them? It seems like an easy fix that will cause the least amount of grief.
Source: Https://us.forums.blizzard.com/en/wow/t/the-new-leveling-experience-and-heirlooms/603129