I have a set of the Bose QC35 headphones (just bought them last week in fact), and briefly poked at the app for it. The one big thing to use the app for is firmware updates (these are noise canceling and pretty advanced headphones). It also allows you to remove bluetooth pairings on the headphones themselves, keeping the set of parings clean. Not stuff I need to do often, so I only install the app when I need it, do the small set of things on it, then remove the app. I thought I may be able to tweak the settings for the noise cancelling but no dice there.
The analog audio over USB-C connectors is a fully-open standard. Doesn't require money to implement, and I think there's not even any needed actives to work with it. Lightning, yeah, that's a closed standard but that hasn't stopped people from making compatible accessories that are unlicensed. Not a great situation there, yeah, but it works.
Thing is, I dislike the 1/8" phono connector and would love to see it go for something else. From a product design perspective it's a terrible, terrible connector. All of the breaking stresses of the connector are primarily on the jack and not the plug, so if put the wrong force on the connector (say a sideways leverage force) you're going to not break the plug, you're going to break the socket. Making more robust sockets takes up a lot of space in devices, and they still break. I'm not saying that Lightning and USB-C don't break, but they are designed in such a way, like micro-USB-B, that puts the breaking stresses primarily on the cable and not the device, the much cheaper end to either replace or repair. But, I don't see things focusing on USB-C or some other existing connector for such purposes.
Well, having a pair of these, I may want an app for my headphones. If it had easier-to-use controls for setting things that are difficult on the device itself, say if there was a set of options for noise cancelling or something like that, sure I'd want an app for that. It's also useful as I said to have the firmware updates done through the app (these aren't dumb headphones). It would pretty much never be something I'd want to use all the time, and my current way of using it suits me well, but with all sorts of devices gaining in all sorts of functionality, you can't assume that no one would not want an easier-to-use interface for their devices.