Its taken me a while to get this downloaded so I've only just been able to watch it. (Downloading video in rural Lincolnshire is painful business!)
There are a couple of things that struck me. Firstly if the number of eccentric orbits of planets so far observed is so great, then perhaps a stable 'inner' solar system is less likely than we thought. I also notice that it relies on a 'passing star' theory to get the really eccentric orbit, rather than the interaction with the 'inner' solar system. (We've had 'passing star' theories before, and they tend to be used when theories are lacking) I also noticed that it wasn't only 'planet 9' which was perturbed by the interaction. If you look carefully at the model, another one of the planets was kicked out of the usual plane of the solar system. (Saturn I think).
So the existance of such a planet is not so far fetched as to be dismissed, but it seems the evidence for it happening here is a bit too 'if, if, if' for me. The trouble with so many 'ifs' is that it starts to sound like the chatter of 'infinite monkeys'.

I use an 11" reflector (Celestron CPC 1100) and a 3" refractor, (Sky-Watcher ST80) mounted on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI 120MM, ZWO ASI1600MC and Canon 1300D for imaging.