And now, Drysc has revealed exactly what it is-- it'll be a "trainable alchemist-only rejuvenation potion" (which means it delivers health and mana), and will provide a random elixir buff to the drinker. And what's more, the elixir buff won't replace ones you already have on, so if we read this correctly, that's three elixir buffs for alchemists. Very nice. And the best part: it's cheap. Drysc reckons it's about a crystal vial and two ragveil. Start saving up your ragveil now-- when 2.3 hits, they'll be in high demand.
Update: The potion is still hard to find on the servers, so we're not sure what the random buffs are yet. Eventually, I'm sure we'll know exactly that this thing does, but for now, all we know is that alchemists are getting a potion for themselves in 2.3.