I hope he is actually the guardian and wants to free Rumple from the dark one curse. We haven’t heard anything about the guardian in a long while so maybe we are just getting back on track. I doubt this, I think it is going to be used to create conflict between Regina and Rumple. Rumple will find out that Facilier wants the dagger, Regina knew this and didn’t tell him or it will be used to get Rumple back on the villainous side. If there is anything that terrifies Rumple it is the thought of being powerless, which he is when someone else controls the dagger, and when he gets scared he usually makes very bad decisions.