One of the issues with Apple's mobile ecosystem has always been the lack of an ability to set default applications. Just this year with iOS 14, users finally got the ability to change their default browser and email app. As spotted by some savvy Reddit users, Apple might be expanding that to include the default music app.
The idea is that if you ask Siri to play a song, it will automatically do so in the service of your choosing. As it stands right now, if you want Siri to play a song in Spotify, you have to specify that the song must be played in Spotify.
With the iOS 14.5 beta, things apparently work a bit differently. After installing the beta, the first time you ask Siri to play a song, it will present a menu of installed music services, and it will remember your choice. Others that commented on the post said that they got a different experience but to the same effect. For them, they asked Siri to play a song via Spotify, and then Siri simply remembered that choice for future interactions. Naturally, the app does have to support Siri.
In our testing, the experience was the latter. It makes sense for the default to be decided that way, because as of right now, there doesn't appear to be anything about a default music service in the Settings app. With the former method, shown in the screenshot, the only way to set the default would be the very first time that you ask Siri to play a song.
Some commenters have said that it doesn't work all the time, and that only certain phrases work. For example, asking to play a song goes with the default selection, while just saying to play music still launches Apple Music. Of course, iOS 14.5 is only in its first beta, so you can expect that the experience will be refined (or removed completely, for all we know).
If you live in the Apple ecosystem of hardware but not of services, this is one of the oldest pain points in the book. Those that use third-party services like Spotify are sure to be pleased with this news, just like those that use apps like Chrome, Edge, Outlook, and more were happy when Apple opened up iOS to third-party browsers and email clients.