Sometime yesterday Jay Young's default feed switched back to RSS 2.0. The world didn’t end, and not everybody cares about such minutia, but Jay clearly does. Jay may be a minority, but this enhancement would enable Jay and others like him to simply drop in a plugin such as this one, activate it, and be on their way.
The patch does not change the default feed format from RSS 2.0. Perhaps that could be considered for a release like WordPress 4.0, and a plugin could be provided at that time to enable users to select the venerable RSS 2.0 feed format, but in any case such a change would require a separate ticket, as this patch does not do that.