If I am tagging someone in my team, I want that person to instantly get an email notification.
Other events in Trello are not worth sending notification emails about.
Is this possible? Or scheduled as a possibility in the near future?
With Trello free and Trello gold, notifications are controlled by individual users. Click your name, go to settings, then scroll to the Notifications area. You have 3 settings here: never, periodically, and instantly.
As long as notifications are set to periodically or instantly, you will always receive notifications when you are tagged/mentioned in a card.
I don't believe there is a way for an admin to force notification frequency in the bottom tiers of Trello, not without a 3rd party integration (such as pinging a Slack user or channel when mentioned).
More information here: http://help.trello.com/article/793-receiving-trello-notifications
Hope this helps!