MK8 Deluxe is basically just what MK8 should have been, out of the package. Not the squid kids and shit, but the ACTUAL battle arenas, etc.
It boggles the mind that there are people who legit say that they DON'T think Nintendo should release an MK9, that they should instead just release more DLC for MK8.
MK9, me personally, I'd love to see them take advantage of the extra horsepower, I'd love to see them actually improve on what MK8 built, but have an ACTUAL battle mode out of the box, bring back Block Fort, etc. Throw in some new characters. There are still plenty of Mario characters that could make great racers, such as Goomba, Magikoopa, Wart, Mouser, Professor E. Gadd, Dixie Kong, etc.
It's neat having characters like Link, having a Hyrule track, etc. But I'm not so sure I want to see it just become "Nintendo Kart", personally. What I'd rather see, in that vein, in ADDITION to an honest to god MK9, is to see like a "Nintendo and Sega All-Stars Racing" or whatever. Don't make an MK clone, make it maybe something more along the lines of Diddy Kong Racing. Have representations from all of the biggest (and even a few smaller) Nintendo and Sega franchises, as racers and as tracks. That would sell a ton. Release it in a different year than MK9 of course. But still...when they started doing the Mario and Sonic olympic crap, I honestly thought it was a no-brainer, what with the Sonic racing games already existing, that some kind of GOOD crossover like that was a no-brainer. But they've yet to do it.
