But obviously he wants us to come up with our own alchemy cards because half the box is empty. That’s why I’ve got so many ways to use potions, or to make it easier to gain higher costing potion cards or to give certain actions that act also as a potion. Hopefully if you played a random game with just alchemy you would get at least one of these new cards that make it easier to get potion Action cards.
While I doubt Donald X has strong feelings about fans trying to fill Alchemy's gaps one way or the other, he mentioned that Alchemy started out as a big set, and was split up due to the German publisher at the time requesting smaller sets (they wanted to sell them in tiny packages, thank goodness it didn't come that far).
What I don't think we know is whether the cards would all be centered around Potions. Taking any other big expansion as a reference point, the answer appears to be no. Even Seaside, which has an overarching "future turns" theme isn't all Durations. It also has tokens, mats, topdecking, and even some off-topic cards. So if you want to fill up the gaps in Alchemy, maybe it would be more rewarding to create new stuff that goes with Potions on a meta level, than just creating more of the same. Potion cards are tricky but powerful, maybe other tricky but powerful mechanics would go with them. And they also have cards depend on each other, maybe that's a thing to explore. Now that I write this, I realize that Dark Ages actually worked with both of these ideas. Or perhaps you like how Potion cards have you pay for cards in a new way, and want to invent something that goes with that (like Empires' debt did), or you like how the set is slightly weird, and you want to do more weird stuff, or you like the magic theme (gasp) and want more mechanics derived from magic themes, like Nocturne does.
My point is, filling the gaps to make Alchemy a better set doesn't necessarily mean you have to create more Potion cards. Having overly many Potion cards in a kingdom removes the tactical consideration of wether or not to get a Potion, and the game suffers as a result. There's a reason Empires isn't all debt cards and Adventures isn't all Reserves.
