The Hoya End Game Boss
I know not everyone here is a gamer, so I want to explain the concept of a video game "boss."
A boss is a computer-controlled opponent the player encounters at a climatic point in the game, usually at the end of a level. Bosses are usually stronger and more cunning than anything the player has faced thus far. Predictably, the end game boss is designed to be the trickiest bit of the whole game. If the player succeeds, they are rewarded with a special visual. (Kind of like a bloom, right?)
What you consider the ultimate Hoya "boss?"
What challenge keeps you up at night, scheming, researching, and strategizing? What is the most impressive/difficult quest on your list? The thing that you are 70-90% sure you'll never accomplish, but you keep trying for anyway.
It could be a plant you are trying to track down/obtain.
It could be a species you are attempting to bloom.
It could be a cutting you have never successfully rooted.