In short, I'd really like to have one of these:
http://amiga.resource.cx/exp/search.pl?product=slingshot&company=
It's an adapter that turns the expansion port on an amiga 500 into a zorro 2
slot like those in the amiga 2000.
They're rare enough to almost never show up on ebay. But they look really
easy to construct. Assuming the card edge connectors were available, I bet
someone with more hardware knowledge than me could make a batch of these for
cheap.
While you're at it, there's a few designs floating around for IDE adapters
for amigas that wedge between the 68000 and the motherboard. A batch of
those would sell out quickly as well.
brian