OK. Well, maybe not run. The only question is whether a religion based on a close relationship with and protection of the natural environment can become a significant world-wide movement. Before you laugh, consider this. Christianity was a minor cult of disaffected Jewish thinkers for a considerable period of time which promoted its doctrine amid increasing hostility from the power that controlled everything important in Europe, the Mediterranean, Aegean and Black Seas for over 750 years. It was accepted as the official religion of the Roman Empire only after 300 years. Without official support from the weakened, but still dangerous empire, Christianity would have been less able to become firmly established. Islam didn't take quite that long - but he basis was the same. State acceptance and enforcement.
The scenario is interesting in that people need religion to fill a need and concern for the environment is a good enough reason as any. As a movement promoting a cause that could affect international policy, the Druids may not find a niche outside of the UK, Ireland or Brittany. But then, in a few hundred years...well.
Here come the Druids. Again. Everyone remain calm.