[...] but suffers from the typical problem that all "virtual Potion" cards do: lack of interaction with Alchemist and Apothecary.
Maybe that Donald's idea of Alchemy isn't perfect?
His concept is sound: Kingdoms with only one Potion-costed cards work. That implies flexible setups, i.e. you are not forced to play with several Potion-costed cards in order to make these very cards balanced.
Weak cards like Counting House that only shine in some Kingdoms are fine as it is fun to find the combos that make them work. Weak cards that require some brethrens of themselves to be good on the other hand are not as their situational strength is pre-programmed (and not accidental like in the case of the aforementioned Counting House).
Maybe that Apothecary and Alchemist are not the standard?
What about if there would be no virtual money? Many powerful cards are basing upon virtual money. So virtual potion is a must too.
They are official cards and miles better than underdeveloped fan cards which presume to be superior to official cards while ignoring basic design principles of Potion-costed cards like the aforementioned "singular Potion card in the Kingdom" concept.
About virtual Potions, sure, you can do them. All I am saying is that they do not work for Alchemist and Apothecary. If you don't mind that, that's no issue. Do what you like.
But many folks, including me, went down the rabbit hole of virtual Potions and found nothing down there. So there is that.
Instead of making acquiring Potions less costly (gotta spend a Buy/gain for them, dead card in your deck) via something like virtual Potions, make the Potion-costed card like the official cards, i.e. "singularly" good.