I live in the netherlands, and i've seen something about this a couple of years ago. Afaik the product never hit the market though, probably because it was expected to be more expensive than just buying the drink with the alcohol taxed.
The taxes on beer and wine are relatively low anyway: On a case of 24 300ml bottles, the total alcohol tax is about 2.5 euro's. There also 19% VAT on it, but that would be on the powder too. On a bottle of wine its about 50 cents in alcohol tax.
Hard liquor is taxed much higher, but you couldnt produce that from a powder and water. The duty on that is in the order of 6-7 euros a bottle, so thats worth avoiding