My main goal: allow to set a follow-up for a ticket (on a specific date), which sends myself (author of follow-up, or assigned agent) an email reminder.

Feature request with general relevance:
Add the 'send agent email' action - as it already exists for triggers - to Macros. That way I can set up a 'send reminder' Macro, which I can trigger via a follow-up. And everyone else gets this functionality too for their own purposes.

(Current workaround: create a macro that applies a label to the ticket, and a trigger that sends an email when the label gets applied.)