Accelerator boards - no future? Bad business?

Remember all the accelerator boards for the Mac, Amiga, and even PCs in the 90's ? I've often wished that I could get something similar on my older SGI systems. For example, fitting an R16k into an O2 or doing dynamic translation on a 4.0Ghz i7. I'm most familiar with the Amiga accelerators. I suspect those who produced them were helped out greatly by a couple of factors. One is that the hardware specs were very well known and full schematics were available for most (all?) Amigas. I doubt the same is true of SGI machines. The other is that many Amigas had processor "slots" (with edge connectors) rather than some tiny fiddly ball-grid array etc... but I'm not a EE; so maybe that's bunk. When I look at these boards they seem like they'd be a LOT of work to develop and produce. I wonder how they were even economical to make back in the day. Plus, now the user base will probably only shrink. It's not a great business model for a hard-to-produce item. It doesn't keep my techno-lust from wanting it, though. So, here's the question. Is my dream likely to ever be possible enough that a boutique shop could pull it off and not lose their shirt on the production costs and R&D to do it ? I'm encouraged by things floppy emulators that are produced for these old machines. However, that's probably significantly easier to make than a CPU accel board. What do you guys think? -Swift