The "skill cap" can be very deceiving. Trust me, just like MK7, the records look incredibly simple, and then you try it. Only to realize you're a considerable amount behind, with no idea why. While the techs and strats may not be as obvious as say, a luck wheelie or spindrift, the micro strats definitely are there and do add up.

Comparing wii skill cap to ds.  

IIRC the mkw luigi circuit wr got to 1:09 on day 1 already. MK8 has already done better than that and actually cut seconds off of its first level record (well technically I guess yesterday was day one, but France has been playing since monday and others got it early too).  

If mk8 were to plateau faster than previous games (espeically mkw and 7) then i'd say it's because of the community getting bigger and not because the game is easier. It is on a currently unpopular console though so who knows if that'll happen

Week one then. I still find the ds/wii thing silly considering how close mkw (a newer game) times are.