This two systems were obtained with different external force, and the nano W/O/W should be dealt with more harsh condition. Therefore, the nano emulsion system with a higher energy, is more unstable than the microemulsion. The result is that the mixture will turn to microemulsion gradually after a long time.
Just a personal opinion. You can try it, and let us know the actual phenomenon.
All emulsions are thermodynamically unstable. Smaller size in emulsions is favored by higher surfactant concentration and production by more extreme shear conditions.