[AI generative Fill in Affinity]

Stable Diffusion from https://stability.ai is available, open source. I really hope Affinity will make use of it soon, or of other AI models.

[Just purchased the package deal...]

For audio, check out Reaper. 

[Stable diffusion integration]

Yes, please add it Affinity :). Right now I use Diffusion Bee (for Apple Silicon) to run Stable Diffusion locally. It's very nice, but integration into Affinity Photo would be an absolute game-changer.