We were discussing at the Aberdeen hackathon that since no entity (organization or individual) actually sponsored it (we're all here on our own dime) that using the "Sponsored by:" line would not be appropriate. When reading the description for "Sponsored by:" in the committers guide, it shows that is is really meant for companies/individuals sponsoring features or developers. We used this line in the past for events since we did not have a separate line for it --- until now.
With this patch, we're introducing the "Event:" tag. It's not "Hackathon" or "devsummit" as "Event: " is a more generic term to use and applies to many events where developers are coming together. I've added a bit of decription to it, including the distinction with "Sponsored by:". Having this line would help us promote these events better in the future and run statistics on these to show how much work is coming out of these events. It may be that a feature started at an event and would be finished by a developer after the event is over, but having this line shows that it is worthwhile to have them.
When approved, we will start using it at the Aberdeen hackathon or after (if we need more time to discuss this), and make a separate announcement to developers.