Its easy to integrate MetaBox core plugin in theme framework but extensions are only available as WP plugins. I have to modify them to integrate in my theme framework and its hard to update extensions in future.
It would be nice if you can improve to load extensions automatically from meta-box/extensions/ directory like Redux framework does. Please consider auto loading extension from a theme directory(specially from a meta-box/extensions/).
Doing so would not break future updates(manual) of extensions. Extensions autoloading and availability as separate WP plugin would make extensions easy to use for developers and non developers
I think using TGM class is still the best way to handle the dependencies in themes and plugins. I'm working on autoload for the main plugin to make it easier to load in themes and plugins. Someone recommended me the Redux Framework, too :).
In the meantime, if you can:
- Use TGM class, or
- Load the extensions directly by including the main file of the extensions (the file which has the same name as the folder), or
- Use a small script like this https://gist.github.com/mathetos/7161f6a88108aaede32a to check if the extension is loaded or not, then run your code.