Image Export Resolution
Depending on what phone or iPad you are using, we cap the resolution to the native camera megapixel count in the phone 6s, 6s+, 4, 4s, 5, and iPod Touch and the same with the iPads. The exception is with the 5s, 6, and 6+ that shoots 8mp. Mextures can edit/export images on these devices at 11 mp.
As Apple increases the memory allowed to each app when it's open, and camera resolutions change, we will keep updating and fine tuning to enable higher resolutions to be edited.