Just a few thoughts, based off an eSport category I have more viewing experience with: Fighting Games.
I think the Fighting tournaments have experienced a lot of these same growing pains, especially as their circuits (a la Capcom Cup) have grown in popularity. I've seen some pretty poor streams, at some major events, so it is something they continue to struggle with (and streaming a video game is pretty easy compared to something like pinball).
A few comparisons of things I like:
1) Scoring: Almost all the Fighting tournaments have a static banner. It shows the name of each player and their current score in terms of wins in the match. Pinball could mimic this. The current game's scores are already being shown. But knowing the points earned, or number of strikes, or whatnot (depending on format) constantly shown means it doesn't ever need to be said.
2) Brackets: This is something the Fighting tournaments have struggled with, but are getting better about. They stuck with paper brackets forever, and it was as awful as it sounds. Now, the major events will, between matches, cut to the bracket. Not the whole thing, usually just zoomed in to the area of upcoming matches. Generally not done until Top 16 or so, from what I've witnessed. But, again, it is helpful. Viewers shouldn't need to be logging into software to see the bracket, it should be a part of the stream.
3) Two Commentators. I've seen more sometimes, and I think it's too much. Just one always seems to suffer as there is no one to play off of. Again, as you'd expect, one does play-by-play, one does color. In between is a good time for interviews or a rules expert or whatnot, but during the play, two is plenty. The play-by-play usually calls out the major moves done, noting when things are ready (super attack ready being akin to having multiball on deck). Color often fills the gaps with playstyle things (Bob is a cautious player who favors precise footsies and positioning over an aggressive offense; Bob hates trapping up and favors on-the-fly shooting and games with fast flow to compliment the approach).
4) Jargon Translation. This is something new that I really am fond of. I do not play Fighting games competitively (I never have), so when I watch the play-by-play, there is jargon I do not understand. The jargon is necessary (like pinball, the games just play so fast you have to keep moving), but I was often clueless about what was being said. It seems this was an issue for others, as now some of the major events are putting up definitions of commonly used terms in between matches (when they normally run their sponsorship crawl, giving the commentators a break). It would be a good place to define things like live catch, trapping up, etc.
Biggest problem I think streaming pinball has cannot be helped. Vertically wide games shown on horizontally wide screens. It really is hard to see much, and since one cannot assume the home viewer can rotate their screen 90 degrees, not really anything can be done to solve that, unless there was a smooth way to track the ball and actually zoom in on the playfield, like what you might do if playing Pinball FX2 or something.