Short answer, no. As long as you learn at least the rank 1 BfA alchemy flasks, you are good to go as far as alchemy is concerned, giving you an additional hour when using flasks in BfA.
There might be some benefit for timewalking in crafting the alchemy trinkets from previous expansions, but I you would need to ask a timewalking expert.
There are also some older potions, often rare drops, that still sell well for twinks and/or are better alternatives to the BfA equivalents. Checking the Undermine Journal for your server might give you a better idea on what to farm for making gold.
EDIT: There is also the dragon archeology mount from Cata?