We might see the new champ in 8.4 :)
Is it me or riot may pull another back to back new champ/VGU release like kayn and urgot. but this time, its swain and new girl champ. Because if you look closely, sometimes riot doesn't give teasers to some champs prior to their release and then you'll just see them directly in the PBE. Another theory is that, riot may pull a kayn to the new champ. Kayn has no direct teasers but he has been teased in the June 2017 Roadmap. This might be the case of the new champ too.
BTW, this is just a theory of mine
PS: I hope riot doesn't pull a prank or pull a SHEN on me in the Nunu VGU. I need a confirmation first in the next roadmap(Maybe around Early April) before I'll write a gratitude letter for them :)