For all of you who want the model stored in files, maybe you should have a look into Bolt CMS.
In Bolt you can configure your content types in YAML files and import them via a migration tool integrated into the CMS.
In my opinion this is by far the best approach. This enables...
versioning of data structure
easy deployment
working in teams (because branching/merging in Git workflows is now possible)
much faster editing of data structure (for professionals) than clicking through UIs
What I miss in this discussion is, what is the audience of users of Processwire?
Do we want to be attractive to professionals working for clients (I would count me to this group)
or is Processwire just another CMS that will blow up its backend UI (like Joomla, Drupal, Wordpress) because it wants to be attractive to users without any programming skills?
My personal opinion is you cannot combine both groups in one system.