AF did it.
Essentially, the A500 trapdoor slot is a cut down Zorro 2 slot wired slightly differently.
I think you get full compatibility, but you only get one slot (IIRC the article did show how a couple could be daisy-chained together but it wasnt easy), and you dont get DMA, and stuff like that. I believe it could take Graphics cards, but the performance was not as good as a true zorro slot.