In my point of view NX will be the Nintendo output for their AAA games, and those AAA games will only be ran by NX. Iwata hints this when he says “we have come to hold an even stronger passion and vision for the dedicated video game system business than ever before”.
So, let’s suppose you log into this Nintendo/DeMA account system and buy a “simple” game. For example, “Rythm Heaven Mobile” (which I would buy today!). This game would be possible to be played on every hardware supported by this Nintendo/DeMA platform.
But, let´s suppose Nintendo releases Super Mario Galaxy 3. I’m sure the company will make it only possible to be played on the NX. You log into your account, buy it, download it into your NX, then play it on the NX or stream the image to the TV. Super Mario Galaxy 3 would be developed by Miyamoto with NX in mind.
In a nutshell, the Nintendo/DeMA is the new Nintendo Gaming Platform to run simple future games and historical backlog while the NX is Nintendo’s new “controller” to run its future AAA games either on TV or on itself (being portable).
We can file this under ‘speculation under what I’d like’.
Nintendo isn’t going to let games be played on very different hardware than what they were created for. Also, sales show that ported games do not sell as well.
If the account system encompasses all these systems, it is possible that you buy a piece of software that it is usable on all. I don’t think this will apply to original software. It may apply to VC games. Maybe.
But seeing how Nintendo puts no effort into VC, I doubt it.