Anyone is free to build whatever they want, there is no exclusive claim to being the first to design any said product.
My problem with designing multis is feature creep and wanting to make the best product with the features we all dream of. Sure, I could just whip up a basic eprom board that only plugs into only MT2 with dip switches to change games and call that 'gud-e-nuff'. But personally I want a better solution using new parts, updating via sd card, game selection on screen, with a full rom board replacement (which includes replacing a custom chip with fpga). I have already built a full scale prototype, has some bugs that need solving, not production ready. Maybe it will turn out that the basic version is what will be produced for the public, a lot less support and investment dollars to do that.