In my situation most of the plans divided by categories and plans within specific category have the same Emails & Messages. Right now I have to customize Emails & Messages for every single plan inside specific category individually which is not optimal. Would it be possible to add Emails & Messages as a category setting to use them on all child plans?
From using this inheritance:
Global Emails & Messages -> Plan Emails & Messages
To use this:
Global Emails & Messages -> Category Emails & Messages -> Plan Emails & Messages
To go further it might make sense to add some other plan options to categories like Fields Assignment, etc.
Just had the code implemented, tested and it worked OK. If you want, you can submit a support ticket and I will send you this version to setup it to your site for using