It looks like the GIMP developers would rather that new feature requests be made on their mailing list before making a new bug:

"An enhancement request should never be filed without prior discussion on the gimp-developer mailing list[0]. This is to make sure that the enhancement requests that are filed are well-specified and aligned with the overall goals the developers have for GIMP."

But please don't let that stop you! The more feedback that the developers get, the better GIMP will be for everyone.

[0]: https://www.gimp.org/mail_lists.html

Seconded. If you are a user, consider actively filing bugs and not expect them to be fixed by the developers without following this process.

Oh, thanks for the heads up. I thought it's for bugs only.