The company I work for has actually been looking into moving to Affinity from Photoshop for other reasons...but if there was a Python API, I'm almost certain they would switch. We aren't an animation studio but we are in the 3D industry and as said above most 3D industry related software (Maya, 3ds Max, Nuke, Blender, and others) use Python as their API language. It comes with so much more functionality through its standard libraries over a variety of subjects and has a HUGE community. Using Python would make Tool Dev almost seamless in these industries (as well as others I'm sure).
This would also set Affinity apart from Photoshop, which uses JavaScript. It's worth at least seriously considering. Python is being used by these huge software companies like AutoDesk and The Foundry for a reason. I'm guessing they didn't just pick it out of a hat.