Briefcase has not had an update for 2 years and it's still working. We don't have any reason to believe it will stop working. The only real change here is that we are being explicit that it won't ever get an update.
There are examples with Bash, PHP, Python for every API call in the docs. See https://odkcentral.docs.apiary.io/#reference/submissions/submissions/listing-all-submissions-on-a-form for an example. There is also ruODK if you use R and we expect to provide more language-specific wrappers and documentation over the time.
I agree that software is getting more complicated rather than simpler, and that's the reason why our small team has to make these decisions. We have a lot of problems to solve for our users and very finite resources to do so. If Briefcase is critical to your workflow and you find in the future it doesn't work for you, consider hiring someone in the Marketplace to make the improvements you need.