Electronically/circuit-wise, almost definitely.
Mechanically/case/housing...depends.
I typically just use an open PCB plugged into the expansion port, without any cover/enclosure. Don't know how well that would go over for active gaming usage, though. For example, my most current effort has RGB output, Hsync out, VSync out, VGA out, Composite Video out, Right/Left audio out, and a socket for a homebrew EProm. (I could easily add a non-volatile memory chip.) It sticks out, unprotected as it were, about 5 inches from the rear of the TG, and is about 8 inches long. Kind of big for convenient usage/handlling by the average gameplayer.
So, what kind of cover, if any, would be used? And, it cosmetics are significant, it would have to attach to the TG cleanly, like the original, which means plastic molding, etc. so it can slide into place. But even if that's not important, you still have the awkward, exposed, rather large PCB hanging out.
Charlie