Mario Karts 8 runs at twice the framerate as SRT, and SRT also rendered below 720p native, so its reasonable for it to have a superior level of detail. With that said, Mario Kart 8 looks clean as hell. A simpler design can be much cleaner, and inherently more visually pleasing for the player. MK8 is very clean, and in my opinion, looks nicer than SRT. Not that SRT looks bad, its looks great, but is muddier and less fluid than MK8.
As for NX and third parties, its really a muddy situation. Even if Nintendo tries to create a console that is third party oriented, this may not be very successful. Why would third parties suddenly flock to the system. I think they will still have a wait and see attitude. I believe some of this stems from the fact that third parties already have two consoles where they offer the premier software. With a Nintendo console, they are in direct competition with everything Nintendo releases. Third party games have notoriously played second fiddle to Nintendo's first party titles dating back to the N64 generation. So is it really in Ubisofts, EA, and Activision best interest for Nintendo to own a large chunk of market share. I cant see a situation where your current COD and Madden gamers jump to a Nintendo consoles simply because those games are now offered there. Perhaps they could have some success with that approach assuming they can severely undercut those consoles in price, but who's to say Sony and Microsoft wont just drop the price even if it results in some losses to keep Nintendo from taking market share. So I am pretty much convinced that they need a concept that can appeal to a very broad audience. Leading the way with a bunch of launch window Nintendo games is the best way to jump out of the gate. Perhaps secure some exclusives with some third party developers who perhaps haven't had the success they were looking for on the Xbox and Playstation platforms. Im talking about developers like Platinum Studios, Tecmo Koei and the plethora of 3DS third party developers. Nintendo has said before that if Gamecube like hardware sales were to be the goad, they would rather exit the hardware market. I think Nintendo is prepared to shoot for a surprise success like the 3DS and Wii, instead of conforming to simply being a me too console and sell sub 30 million units.