I made a video a couple of years ago called A Tale of Two Macgillivrayi; It is below for those who have not seen it.  I compared two of my Hoya macgillivrai with one grown in a tent with perfect lighting and humidity and said that it was impossible to flower one in the regular house without supplemental lighting:

Well, what I thought was an impossibility might just happen.  My extremely large plant in a north window with no supplemental lighting has one single very weak looking bud as can be seen below at the top of the photo: