The idea of the NX using cartridges makes me think...
...Should cartridges come back?
Space is no longer all that big of an issue for them and thus perhaps the higher speed, more reliant and cheaper benefits of them (actually might not be cheaper with the newer tech, need to look this up) could make them the better option.
Yes, discs still provide more space, but nobody uses all of the space on them now (besides Square Enix BS hypothetical situations).