The first suggestion I'll make is one I'd bet gets suggested often, and that's a film strip system for Pixelmator Photo. The film strip in lightroom is your batch of pre-processed photos in your collection, and it's a huge benefit as it means moving between photos doesn't require you to leave your current editing tools, and is basically instant as every image in your batch is pre-rendered and ready to be edited on. I don't have any great ideas on how to implement this into Pixelmator Pro as the new(-ish) tabs editing system is kinda close to it, but in Pixelmator Photo it could either be a menu on the opposite side to the level adjustments, or it could replace the presets strip at the bottom of the screen. I think this change would make editing many photos by hand on Pixelmator Photo way faster and make it an easier switch from Lightroom CC users.
My second suggestion is keystone geometry editing. As someone who does a lot of street and architectural photography, I may value this feature more than others, but in my opinion it's the strongest lens correction setting besides crop. Keystoning, in case that's not the term it's best known as, is a geometry editing system that has the user draw two straight lines on surfaces they'd like to be parallel, and the software runs an algorithm to take the perpendicular lines in the image and make them both either perfectly vertical or horizontal. (This first made an appearance in Photoshop but is present in lightroom.) This tool could fall under the crop settings in Pixelmator Photo, and under the Crop tool in Pro, and would give those who just want to straighten out lines the best and easiest method of doing so in a pinch.
In no way are either of these changes necessary, just two suggestions I think could get even more powerful tools in your software. Thanks for making the best photo editing apps ever!
- Samuel (P.S. Pixelmator Pro for iPad when ;D)