You've already got the potion and the idea of putting it in a container to drink in the field. You've also got leather flasks and metal bottles. Is it such a stretch to realize, "If I put this flask inside my helmet and pull the cork out with my teeth, I won't have to drop my sword and shield to fish it out?" That's an innovation that a single person could devise, requiring neither special knowledge nor lots of money to attempt (assuming you're smart enough to fine-tune your design with flasks of water before taking it into battle).
An idea that looks good on paper (or on an Enworld post) can turn out to be an absolute catastrophic failure in practice, and I'm confident a potion helmet falls into that category. The whole process of custom blacksmithing armor and testing that its battle ready is going to take a while and some money. One big problem is that rubber tubing and plastic tubing and reliable sealents were not invented yet -- is your adventurer going to invent those too? This isn't Star Trek ('oh if I just decouple the rubber tree from the dilethium I should be able to have a working prototype by the end of the day'). I can't even envision a clunky contraption that allows you to pop a cork out with your teeth. How do you think you'd feel in an oversized helmet working your lips around a cork in your face while a giant is trying to whack you with a giant baseball bat? What happens if you build the stupid thing and you don't find any more healing potions at the local dungeon treasure dispenser/vending machine?
Your sig is about "realism = internal consistency". In my game, "internal consistency" means:
1) adventuring is not a common "career" -- there are not enough adventurers out there to support a fully-fledged adventuring cottage industry, the market is just too small
2) the tiny adventuring customer base is too unreliable -- customers die a lot, move around a lot = lack of repeat business and long term customers, and once the local dungeon is cleared out, you have to hope for a new local threat to the town!
3) adventurers cannot rely on a steady reliable influx of magic items on demand, they're scavengers and treasure-hunters, not ordering pizza
4) it is a world without modern sensibilities, and magic has its own arbitrary laws that we don't understand
5) it is a world where combat is a serious and deadly, and a wonky helmet can get you killed. Period.
6) overall, if you weigh the pros and cons of the potion helmet, the obvious common sense is to drink your potion before or after battle
7) the 4e 'gamist' encounter design (assuming buffs during combat instead of before/after) does not make any of the above less true
And the less common healing potions are, the fewer "innovations" of this type one is likely to see.
The more common healing potions (and especially adventuring), the closer you get to a cottage industry springing up around adventuring and magic items, as I parodied in post #35.
yes... the argument about how magical any given world is would determine exactly how many different forms it would take... but if we are talking the typical D&D fantasy world... the one where the magic items found within the Player's Handbook and Adventurer's Vaults are assumed to be real and accessible items to PCs, both in retrieval and crafting... to think that the artificers would not figure out how to make these items better, cheaper, and more useful is an attempt to maintain the tropes of classical D&D magic while not acknowledging the science, business, and evolution of it.
If magic could be engineered to be so flexible, then spells would be equally flexible. Every wizard would be like Green Lantern, able to weave strands of magic to create anything he has the intelligence to imagine and the willpower to create. But that's not the case. There is some arbitrary reason why spells are 'pre-programmed' into individual discrete effects. Those arbitrary magic laws apply to magic items as well, just for different arcane reasons probably involving vessels and attunement.