I would say Nepal is of vital geo-political interest to the US, especially more so with the burgeoning  superpower status of China and rising economic might of India.  Given that, the US will support any system that can meet its needs in the region.  The political parties have proven to be unstable and fickle.  If the monarchy can be brought back to life, this might prove to be beneficial for American interests.  Whether that is good for Nepali people is whole another story.  Methinks.