Best for me would be a per-journal option to opt-out of birthday notices (for example on a fictional character account, as well as memorial). But that's unlikely to happen, unless they switch to the subscription model.
Second best would be the ability to opt-out of birthday notices for $category.
Acceptable would be the status quo, where you must take them off your circle in some fashion to remove reminders. I am one of those people who are not bothered by these at all.
Detrimental would be any sort of opt-in for memorial accounts, removal from birthday lists, etc.