Recently I've bought a couple of old Dutch Club Nintendo magazines.
One of them (which is from October 1995) has a review of Obelix (no, not Asterix) for NES. 

Unfortunately the review only shows pictures from the SNES version of the game but they were certainly writing about a NES version, proved by the following sentence in it "Was hij al verkrijgbaar op de Super NES en de Game Boy, nu kun je er ook met je NES tegenaan".

Which translates roughly to "The game was already available on Super NES and Game Boy, but now you can also play it on your NES"


Is there anyone here who has ever heard of this unreleased game?

I believe they're referring to "Asterix & Obelix", as they go hand and hand with each other. However, I could be wrong... a new prototype nes game would be sweet! Also those mags sound cool

Yes it would have been a NES version of the SNES game "Asterix & Obelix". I think the Game Boy version of the game is just called "" Obelix" though.