Hi Bryan,
Thanks for discussing this with me. Regarding the technical details on how to achieve this real-time collaboration, I don't know, perhaps you know more about that. Having it work cross-platform is ideal of course. All though Affinity already supports iCloud which is an apple only feature too so depending on how hard it is to integrate, it could be a platform only feature to I image.
When it comes to live collaboration vs. async collaboration, I believe live collaboration simulates the actual real world more. Working together physically is actual "real-time" and not async. So to that end I believe that how faster you can get feedback on the work that you do, the better the collaboration will be.
I can image that you don't see the advantage in a feature like this, but I think Google Docs showed that real-time collaboration actually made a lot of sense to people after it was introduced, before that feature people would say; why would I want anyone else to type through my sentence. Users will find a way to make use of the real-time capabilities and will like it because it shows an up-to date version of the document/model/file that they are working on. As lots of tech companies would say; "it keeps everybody in sync".
I can imagine that in Affinity Publisher, it would be great to see in real-time that others are working on different slides. Really feeling that together with colleagues you are working towards a certain goal. Perhaps Photo and Designer are a bit different but I believe that it reflects the real world way better than async does. I myself work in a big design office in The Netherlands and always work async. I would love to work more collaborative with my colleagues.