Serenity Caldwell, iMore:
The beauty of Apple's current software theory is that newer, more professional features can easily be built upon the current foundation. It'd be pretty easy to add more custom adjustment widgets down the road, for instance, or work more brushes into the Repair tool, or integrate third-party app extensions into the program.
But that doesn't mean Photos will ever be the app for true professionals. Nor is iMovie likely to help make the next Sundance-winning film. But they're built in such a way that they can help users transition more easily to software that can.