Dimension 20 On A Bus is a Landscape-Altering Masterpiece and No, My Name isn't Shirley

 It's a kind of magic what Katie Marovitch Accomplished with so little. I am fairly confident even she doesn't recognize what a huge impact this could have on the hobbyspace overall, birthing a new style of play (or at least a game) while being otherwise utterly uninvolved in the scene beyond her professional career with Dropout.

Neither is My Name Willis

 Obviously a significant portion of that was done as half-sketch, half-improv for the sake of making an easily engaged and super shareable comedy clip. Even if it turns out to be a backdoor pilot in the long run, my guess is the idea began and ended at that clip at least while it was being put together. But it is often in the carelessness of passion which we can create something more profound than intended.

 Though I wouldn't recommend actually copying the particular method which Katie took to "GMing" for the clip itself given the absolute abstraction leads to frustrating amounts of non-communication and practically zero bits of actionable information, I do see there is an amount of Calvinball-esque childhood wonderment and approachability bordering on levels magnetic which is inherently tied to the act of play. Something we can tend to lose or often is expressed as needing the approval from an otherwise intensive rulebook made by a corporation that cares more about you as a dollar sign than satisfied individual. Something you may think is antithetical to my whole ordeal here with Mechanized Make-Believe.
 Lemme put it another way: What game were they even playing?

 Well in the pitch Katie sold it as Big Name Game¹ and I know you would never be so boldly foolish to make an argument which uses the non-design of "rule zero" to defend it as such, since it clearly and simply isn't that ruleset by any stretch of the imagination. So then it only stands to reason they weren't playing a pre-made game at all.

You Want Something Done Right…

 In fact, all the elements of the "system" itself came from Katie effectively tossing down a smattering of random, what we will loosely define as "game components" for lack of better terminology then interpreting how to both use and what that meant in the moment,, while Mark "Fake Fans Call Him Matt" Mercer attempted to complete the narration and make connections to otherwise intentionally disparate elements. And.. You could do that, don't ya think?

 Actually, when I first thought up the concept of Titterpig Potluck I had also considered an extremely similar version, some might make comparison to another, much older playstyle² though it is absolutely different enough to deserve its own name.. Maybe an homage Katie's masterpiece in there.. OH!

Tabletop On A Bus

1.  Collect some objects which one could easily hold between index and thumb, enough for each person at the table besides yourself. These are your "Game Pieces."
2.  Collect a singular, larger object which the above Game Pieces could easily rest upon or within. This is your "Play Area."
3.  Collect at least one or more things you can engage for stimulation and output. This is your "Component." EXAMPLES: a six-sided die, deck of cards, voting ballots, bingo boards and ball roller, darts/dartboard, cornhole, a metal tub full of water and apples, sack of fortune cookies, etc.
4.  Collect a group of people. Establish boundaries and a means to avoid unfun topics with minimal conflict/confusion. Then declare who amongst you is the Bus Driver, the remainder are Passengers.
5.  Passengers acquire (randomly or by selection) a Game Piece each. This is their character. No, literally. OPTIONAL: Take a moment to establish a feature or two of said characters granted by these provided forms.
6.  The Bus Driver gives the briefest explanation of where the characters are while presenting the Play Area then may demand engagement with the Component if what happens next cannot be determined or to prevent boredom from settling in.
7.  Go until the Play Area is destroyed or enough agree it's been fun but Oh, would you look at the time.

 And now you're off without giving a lick of capital (economic or social) or credit to a company that cares about you only as a farmable resource! Isn't that great?

¹You know the one. Double Ds but less fun to play with. Owned by a billion-dollar company. Tom Hanks' first leading role- No that's not right..
²Suggested Reading: Free Kriegsspiel: Worlds, Not Rules, Etc. by d66 Classless Kobolds