A theory

When they announced the new support champion they showed a picture of a book (the picture to the left) & I noticed its pattern looks similar to the pattern on this tree (the picture to the right) & that tree is in a place where yordles live. So my theory is that the new support will be a yordle.

Some bonus evidence: Riot said that they are working on stories about yordles right now which is some evidence to my theory because it makes sense that they would want to make stories that their new champion is involved with