I'm a digital artist who would like to use Affinity Photo in my Workflow. I work on a large Wacom Cintiq and typically use a 3D Mouse.
Contrary to it's name, a 3D mouse is useful for much more than just 3D Work. 3D Mice are a knob like input device that can take input on several axis/motions (eg, pushing up down, side to side, rotating, twisting).
If there was 3D Mouse Support, I could easily work with my pen, moving the canvas around using the 3D Mouse in my other hand. I could rotate the entire canvas whilst I work by twisting the mouse from side to side, dynamically zoom the document in and out by pushing the mouse downwards or pulling it upwards, in the same way I do as I work with 3D documents. This would be a very ergonomic solution, especially for people like me, who do not have newer, touch capable devices where tasks such as zooming, rotating canvas etc are tasks involving several steps that require keyboard or mouse input, both of which devices are difficult to keep in arms reach/use when you have a large tablet screen right up against you.
My 3D Mouse is a 3DConnexion Device. 3D Connexion Devices could be supported natively by your software, or you could accept Joystick input for zooming/rotating/panning the canvas, which most 3D Mice including mine can emulate and this would be a solution that anybody can use and would make Affinity more accessible for people such as myself.