Why would not use pack.source.builtin translation string instead of plain "(Global)".
Or maybe it would be possible to add localization string for this?

Also would be nice to have an ability to change the color of the description. For now it's always light-blue, even if description has color value in mcmeta.

Why would not use pack.source.builtin translation string instead of plain "(Global)".

Because those aren't built in packs, even if MC treats them similarly, people will get confused.
I can localize it though, just hasn't been brought up yet.

As for the description? I would have to take a look at it. I thought it would just use whatever is defined in the mcmeta of the pack.