Up to two years ago, I definitely would have bought into that. Memory was the thing I most needed on my A3K. I wanted to find a DKB3128, but those boards are hard to come by!
Now I've moved to Amithlon and memory is not a problem for me anymore. Now the problem is that my PC is too slow to run hardware-banging games and demos properly in E-UAE. But that means that my classic hardware is still useful.
I agree with other posters that the thing the Classic market really needs at the moment is more PPC cards. Those should take modern memory modules.
The Zorro III memory card might still be a good idea. I don't think it should be difficult to make one. How big is the market?