I think it's a bit of a stretch to regard the N3DS as the first and only 9th generation console developed and on the market, but I'm assuming that was not the question so much as whether the N3DS should be considered by consumers to be a new platform.
I see no indications that Nintendo is planning on phasing out the 3DS/2DS, or for 3rd party support to ramp down as well in favor of N3DS support. Nintendo could announce that the next Mario Kart, Mario Bros., Smash Bros and Zelda games are N3DS only, which would signify the former, but they haven't. It sounds like at most, in the interest in selling to the largest consumer base, there will be additional features or output modes (hardware enhanced) for games that take advantage of the updates, while still being playable on 3DS hardware.
I consider it a new console, even if it is more of a .5 update like a S model iPhone. It's definitely a bit more of an upgrade than the DSl or DSi, which were strictly redesigns, due to the upgraded specs that make games that require the faster hardware and additional memory run only on the new hardware.







