There's some confusion (it's probably mine). I'm under the impression that visual voicemail is the email like app that lists your voicemails in an email like thread list but you still click on each one to listen to it. Voicemail transcription I thought was called just that, transcription. To be clear, my problem is simply being able to visually see a list of voicemails and what number they are from as the standard GOS phone/dialer app provides.
If I'm wrong on the terminology be sure to let me know how stupid I am. You'd be right!
As far as the hijacking, just like Pand-na so bluntly pointed out, don't worry about it. with this thread I was actually looking for more of a discussion on this kind of thing in relation to open source projects. In my experiences with them, they last as long as there is a big base of "leaches" (for lack of a better term). Sure, I've always gotten involved and contributed because I was interested in a particular aspect of a project, but any of the projects I worked on where it was only to fill a need or desire of the instigator of the project (which has been me sometimes in the past), the project never lasted.
My view on the topic is that cell phones are pretty much mandatory at this stage of western society and the two major players, Google and Apple have reach well beyond benevolence in their surveillance of the customers and GrapheneOS was an elegant and viable solution to that, both technologically and the fact its FOSS. I for one would like to see it persist, even if the original creators get tired, or bored, move on, whatever. For that to happen I believe there needs to be a large base of adopters and a smaller but steady stream of contributors. To keep adopters around, I think there's a core set of features that they will likely "demand" (or move on to some other solution). For me, I could care less if the visual voicemail works but for the handful of people I was trying to talk into ditching the surveillance for GrapheneOS, it was very important. I try to listen to others and not just decide that since something is unimportant to me, it isn't important. A user is either going to use something or not. I personally would rather their use than their hitting the road because I believe in this project. I think a core set of features is important to the longevity (and I think the core GOS team does too from reading their wiki entries). @Murcielago brought up funding as another key aspect for longevity.