Here's a thought:
Since you don't yet own any Hoyas, why not just start a thread in the Houseplants Forum and ask folks to share photos of their plants on the thread. Hopefully you will get a good response and then, maybe later, the group that shares discussion on your Hoya thread can bring up the idea of a forum.
Edited to add:
If you go to Google Images and type in "all things plants hoyas" you can see tons of photos. Hovering over each picture will show if it is on our ATP site.
