export/import project file via iTunes File Sharing
So you've worked quite a bit on many projects, and it's starting to eat up the disk space of your iPhone. You need to delete the projects to make space, but you want to backup the project data (with layers, masks, foreground&background photos intact) so you could work on it at a later time or use it for reference. There needs to be a failproof way to backup and re-import the project data, and that would be thru iTunes File Sharing.
Currenly, Union does not support iTunes File Sharing. This is a basic iOS feature, and should be a required feature more so for "user created content" apps. I don't see what reason Pixite could have to not support this.
If project files can be backed up and imported via iTunes File Sharing, then the other request from a user who want to be able to share projects between friends would be achieved as well.
And no, backing up files via iCloud would not do. I can't confirm whether Union backs up project files to iCloud, but even if it does, iCloud is not failproof, while iTunes File Sharing is.