I've never watched simultaneous play, but I would think it would be hard for non-pinball players to follow the action...and for commentary to keep up.
Lots of people watch the olympics. Some sports are played simultaneously (like swimming), but others are individual time trials like downhill skiing.
I could imagine a goal of "Well Walker MB", and having like 10 people run through that serially...with commentary for each player. On the side is a list of the players who have already finished, along with their qualifying times. That could be interesting. Announcers can talk about different play styles as they come up, etc.
Well Walker MB might be a bad example because it will just be a flail fest. If we're talking Walking Dead, what about "Score a mode triggered Multi-kill"?
Maybe there are multiple events, and we see the same set of players play through all of them. Or each round could be different objectives on the same game. In some sports (like ski jumping), people get multiple attempts...so maybe that is a thing. Or perhaps you get X number of re-attempts spread across all objectives, and can use your re-tries as you see fit?
If live broadcasting is important, then picking short objectives, perhaps even with a time cap, would be good. After 4 minutes (or whatever), you get a DNF, and can use a re-try when it gets back around to your turn.
Also, live broadcasting might be a reason to do different objectives on the same game (to reduce switching time). Imagine Tron, where there are 4 rounds...each one is to complete (light solidly) the designated mode: Clu, Zuse, Quorra, Light Cycle (I picked these four because doing all 9 modes might take a little too long, and some of them won't be that exciting...like qualifying disc, or shooting Tron targets over and over). I imagine this might take about an hour for four people to do.