One comes with all processes & is standard. What standards if any would we use if any for holding config in services? gRPC with config defined in app-specific/bespoke protobuf schemas? Custom OpenAPI per app?
I ask myself what is thr known quantity that will have the nest tools & support & third flexibility. Given how vast the support base for env vars, how well known they are, and how miscellanious & varied & small-fry & specific most alternatives would be, it feels like a lock.
The only thing I can think if as better & more scriptable is directories of small files. 9p esque filesystems. Cause wow are we good at managing filesystems. But we're at risk of having too many ways to use them & too many tools to have a clear & shared forward path.