> There are many opportunities to retrofit old systems of all types with modern low-cost embedded technologies.

I'd leave out the "old" there.

An example: Friends work(ed) as engineers in theaters and music-venues. The costs for (DMX) equipment is insane. Some lamps, rigs or controllers are so expensive that shows only rent them. While there's lots of cases where you don't want to cut costs¹, quite often a cheap variant cuts it just fine. So apparently there's a lot of Pie's, Arduinos, ESP32s and old androids used to handle stuff. Custom, hacked, duckt-taped solutions. All of them are certain a startup offering generic but cheap modules that engineers can customize, would be an instant hit. Especially if "service" can be bought with it.

Or a friend who installs (climate) control systems in (food)factories, who cludges together arduino's and some hacky web-interfaces, who is certain that the industry would love some "off the shelve" solutions that installers can build their own hardware- and user-interfaces on is a very much wanted product. The industry (in EU) is according to him, one built on "lock ins", where a factory starts off with AcmeInc controllers and then slowly Acme will start charging almost "extortion-fee" alike figures just to fix stuff on a sunday night.

Or, a friend who has a fruit farm with lot's of freezer-storage (running hundreds of KWs), whith whom I cludged together some Arduino's and home-automation to control the freezers to run when electricity is cheap or free. Stuff like this is available for consumers at reasonable prices, but the moment the Amperages go to industry-level, the costs explode. Where a simple remote controllable power-switch can cost €1000s. I'm certain that there's hundreds of thousands of small warehouses, supermarkets, traders, logistics that could save a few hundreds to thousands of €'s a year, by controlling their freezers, heaters, pumps, pressurizers, dryers and whatnots smarter with "turn key" modules built from generic low cost hardware.

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¹ relevant: There's a lot of "Nobody Ever Got Fired for Buying IBM" behind it: if you go for the cheap €800 chinese knock-off and mid-show something starts failing, its your fault. But if that €10.000 controller starts failing, it's no-ones fault.

With respect to bowling alleys, for things like professional shows or food safety it's a bit more than "nobody got fired for buying IBM". The stuff's gotta be able to survive field conditions and not cost millions of dollars in refunded show tickets or spoiled foods. Manufacturers test and make themselves accountable for this. Cheap, customized modules work until they don't, and by then the engineer who put the custom system together in the first place isn't there to fix them. Who would you call when some quick-and-dirty integration code that was burned into these embedded modules without ever being put in a source versioning system fails in some weird edge condition? OP is an SRE, it's ok for him, but the average farmer or show operator doesn't have the skill.