From Venture Beat:

When you start an online match of Mario Kart 8, you get an option to either go play with the original 32 courses or with all 40 courses (the original 32 plus the eight DLC tracks). Likewise, when you create a tournament, you can select 32 or 40 courses, but you can also select to only play the DLC levels.

Of course, if you make a 40 course tournament, everyone that wants to join will need the DLC.

But you will never come across a situation where someone will get kicked out of a lobby because they don’t have the new content. People with the DLC will also never have any disruption to their experience because other people didn’t get the new courses.

http://venturebeat.com/2014/11/06/heres-how-mario-kart-8s-downloadable-content-works-online/

Basically those with the DLC have a new online mode to play with that lets you choose all 40 courses. Hopefully there will be a lot of people who choose this so the lobby won't be empty!

Mhmm, makes sense! I believe thats how virtually every other game does it so its nothing new and I am sure there will be tons of people to play the DLC with considering how great of a deal it is

sounds good.

so if I use Link and no one else has Link everything will be fine.

Good to hear.
Everything else would be a huge let down though.

Awesomeness!

Ah, Rol. We'd get along so well if I didn't disappoint you so. :P

What about when the next DLC comes out?? Then we will need an option for 32, 40a, 40b and 48 O_O
The online players will be so split it will be like trying to play a Wii game online in 2014 =P jk

There's plenty of players, and most who got DLC should have all 48 with how good a deal it is to get both packs together.

Naw really!?

Feel free to explain yourself anytime!