A company called GamesCare has created their own version of the Sega Neptune called the GF1 Neptune

A Neptune was going to be a Genesis / MegaDrive with a built in 32X, so yes, there are plenty.

There are typically quite a few to choose from at this point in a console's life cycle

Youtube Trailer says FPGA.

... though the article says that SegaCD support will be from external hookup to the official SegaCD device. So I guess it's just MD/32X. I was really hoping it might have the full suite.