We have started to do some things with snapchat, although nothing with cartoon overlays (filters is the industry term).
Snapchat *does* take live video. Create a quad and a new material, and select 'Live Source' from the layer options.
We then insert the graphics we create for snapchat content.
There are also programs to rotate your live source, so you could run this through your switcher, eliminating XPression from having to handle a live input.
So that workflow would be: shoot in 1920x1080, create gfx in 1920x1080, but rotate everything 270 or -90 degrees. It helped me to have a rotated monitor when we did this.
Then shoot your footage and rotate the footage in post or through the software. Sorry I can't recall the name. Maybe movie recorder?
#XPression