You can reply to Which missing apps and features do you want in Nextcloud? and we can break it out into a new topic. 
Or, post under #general category.
Developers will see the suggestions, but as you mention it is not a formal process. The developers have made it clear that they do not wish to receive anything beyond informal suggestions, bug reports or pull requests. The idea is anyone wanting something bad enough can code and submit it themselves to the appstore.