Im assuming yes, but I want to be sure

Probably. However, the DLC first needs to be played and evaluated on what to actually do with it.

It's hard to say at the moment given we don't know what format the DLC is in

If it's more levels continuing the story, then it's possible that the currently existing levels + the DLC levels could become the new "All Stages" category

Ultimately though, it's up to the community as a whole and what people like running. I'm sure we'll have plenty of discussion around when the DLC comes out