I’m saying you shouldn’t create a new URI scheme yet. You can achieve what you want, now, without one, and using a MIME type initially will let you get valuable information to inform a future, better proposal for a URI scheme.
It has the AntennaPod brand name in the technical stuff. If today AntennaPod implements the caller side and tomorrow Fedilab and Subway Tooter implement reception, then what should Funkwhale for Android (FfA) do when I ask them next week to implement the same functionality? Use the AntennaPod branding in their code?
First, it’s not “branding”, any more than an app processing the “image/jpeg” MIME type is somehow “branding” the code with the Joint Photographic Experts Group.
Second, yes, if FunkWhale wants to achieve the exact same thing then they should use the same MIME type.
There are two reasons why they might not do that.
a. They consider it a branding issue. If they come to an open source project and say "Hey, we want you to duplicate this code that you’ve already got, but use audio.funkwhale instead of org.antennapod[1] then see point 1, and they’ll get laughed at.
b. They want functionality that you don’t want[2], and/or is not expressible in your content:// URL schema. In which case they should first be encouraged to work with AntennaPod to extend the schema in a useful way. Hopefully AntennaPod and FunkWhale work together constructively to do that. If they don’t, FunkWhale can approach the open source projects and say “Hey, we’d like this functionality, we tried to work with the AntennaPod folks with it but they refused to add it to the schema, so we want to send intents with vnd.audio-funkwhale to express that. Here’s a PR.”
Either way, after some time has passed we have real-world experience with one or more Android intents that use the vnd. prefix, and that experience can be used to inform a future FEP.
[1] My previous message used application/vnd.com-antennapod as the example MIME type, I should have used org instead of com.
[2] This is why I’m wary of your claims that this will only have a very small set of use cases. AntennaPod might only have a very small set of use cases, but other apps might have a larger set. Doing a trial with a vnd. prefixed MIME type allows you to discover those use cases safely.