Hi Ljabli !
I've been meaning to add formal support for multiple cameras for a while and what you mention is exactly the way imageplanes are planned, unfortunately I haven't had time to finish it off yet, but it is very much on my TODO list.
Technically it is currently possible to load cameras from Alembic files, I added support for this as it should help doing digi-double work on the app. This was added on the backend so it isn't documented on the website, I just ran a quick test and realised that I never exposed the "Look Through" button of the cameras so they load but there isn't a way to look through them, let me see what I can do about that... 😉