There is also second keg of beer you can poison later in game.

Ooh, looking forward to finding it (on BG3’s release).
It’s in EA now! (Though it’s a bit sensitive to timing in my experience.)
I asked for other mixures sometime around Patch 2-3 ... seems like Larian didnt find my idea to be good enough.

The ideas you cite seem cool and not so much work. The pseudo cut-scene with the goblin’s toast to the absolute already exists, as do the potions’ effects.
Yes, would be great if all goblins drinking got the effect of whatever potion you put in the barrel! Though not sure the duration should be longer than normal so potentially only real long-lasting potions would be useful in the grove attack.