DISCLAIMER: I am not a developer
Polotno integration into nextcloud… Seems a good candidate for canva-like funcionality into nextcloud , would it be feasible?What would be needed in general terms?
You mean https://studio.polotno.com/? At least according to the sources it is released under MIT thus releasing under AGPL (as required for NC apps) the combined app should be okay.
I have not check how one could integrate the app into the Nextcloud server ui. That might be doable somehow.
I see the bigger question: why would one do it? What data is stored permanently? How is this stored? In a DB or as files? Can this be altered programmatically?