Who knows, perhaps without the cd add-on, they would have made a first for cartridges... multiple hu-cards for 1 game...
It could have worked similar to multi disc games, where you need a save file at the end of the first hu-card before you could play the second hu-card... and of course, if you try playing the second hu-card first, you would have gotten an error...
I think that idea could have worked... and who knows, maybe nec would have been the first to do so... by doing that, in a sense, you could really get the same as a cd, with the exception of the audio... which I dont think would be be nearly as good as cd quality...