I personally don't think that would have worked. We've seen repeatedly from multiple companies that selling anything as an "addon" just results in failure because developers can't assume that people will have it. You have to bake the function in the lowest SKU or it ends up a novelty.

Perhaps if they rolled out the canceled Neptune as the half-step between Mega Drive and a delayed Saturn. It would have been the an excellent base SKU developers could target, with cheaper CD media as a bonus... but I just don't see an enhanced Sega CD/32X going up against the PS1 and coming out any better than the Saturn did. I guess they wouldn't have hemorrhaged all that money on wasted hardware though.