Didn't find anything about this topic, so I'm proposing it as a new feature.
I recently found this video: https://www.youtube.com/watch?v=n3aoc36V8LM
which explores the capabilities of something called PatchMatch found here http://gfx.cs.princeton.edu/gfx/pubs/Barnes_2009_PAR/index.php
What it allows is to define simple geometry to help the algorithm patch or reshape certain areas of the image.
I'd love to see this implemented in Affinity Photo. Seeing as it is open source I hope it would be easy to implement.
I hope I can get some feedback from a developer if this will be implemented at some point in the future.