Yeah, I watched that run live and also commented on it on Reddit already, but also gonna leave my 0.02$ here - especially since it's on the frontpage now.
Great stuff. It's been known for quite a few seasons now - Reddit user "HerpDerpenberg" made a leveling guide about this method in more general terms - but as usual it takes someone to actually showcase this. I know many people who have been testing this for weeks now.
Just a thing to keep in mind:
This method requires to reset games; maybe only every 5-10 minutes, but if a very large number of persons does this, there is a realistic chance that the servers go ham on season start. I've had a discussion with Desolacer about this and he said it should not be the case, but I personally have a plan B just in case queues show up, because nothing is worse than sitting in menus on season start for 10 minutes. Also keep in mind that he's playing HC and the server stress there is much lower, but on SC I expect many people (especially solo players) to do this and the servers might go nuts in the first hour of the season or so. Basically, I strongly recommend against running *only* FoM (there are many more areas that work well if you practice a bit, and it also spices it up a bit as pure FoM makes it super boring) or just go rifts in case, which is also great for gear (which you will definitely lack by doing nothing but FoM).
Also, as in previous Reddit threads around this methods, I'd like to remind that for groups rifting is probably just as good as the streaks are difficult to maintain in groups. A full group that tries this without practicing will be better off rifting at season start.
But yes, in general this is something that can really spice up things. But it needs practice, you cannot just do this on season start and expect to be faster than in your regular rifting group (you'll most likely be slower and might be at a disadvantage in terms of resources compared to rifting).