I would really like to see the following:

Reminders function under Actions in both tickets and invoices (Invoices often times need to be modified or questioned by management after an employee mistake).

Reminders history section (or just the existing bottom part) so you or the manager can see in the ticket/invoice/client section the ones that were done or not.

Force notes upon completion of reminder (admin optional on/off)

Keep functionality where someone else can assign a reminder to another person.