If this was my hoya (I'm no expert): the part that is yellowing looks like it is a dead end. I isn't putting out any new growth. I would either cut it back a little to see it that jump started growth on that vine OR just cut that vine off. Because it is not actively growing the plant does not send nutrients to that area. Tip dieback can be due to a build up of salts. You could try flushing to soil to remove build up of salts. That would be easier that repotting.

I think I'll repot it. I thought about chopping but I'm going to do that if things get a whole lot worse... This specific vine has about 3 peduncles on it and looks so pretty when it blooms. I just want it to make it :/

Try giving it a foliar feed of a kelp extract based fertilizer at 1/4 strength (or whatever you normally use). My imperialis occassionally starts yellowing, and this helps more often than not for it to green back up.