Finally managed to find something that shows off the character select screen from the recent demo events! Funnily enough all I had to do was type "Mario Kart 8 character select" into google! Anywhos, what's shown here is a bit concerning, as it would mean there's only 3 unrevealed characters left if 30 is the final amount, yet there's so many characters still who're likely to return, such as Bowser Jr,, Birdo, Dry Bones, Diddy Kong, Dry Bowser, and King Boo, and it's pretty hard to believe that the Koopalings will be the only new to franchise characters. However, if I recall correctly, a new row of characters wont appear until you've unlocked someone from that row, so let's hope there's one more row of characters that just didn't have anyone unlocked for the demo. That'd put us at a good 36 characters if this is the case!
Here's the original source of the picture, which shows up at 6:58.
http://epn.tv/all/type-of/shows/april-7-ep-daily-full-show/
The cup select screen is also shown off at 5:16, but it doesn't really tell us anything new from what I can tell. I still just wanna see the Kart customization screen!