Having played with the REST API for some time, I noticed that the community and collection endpoints miss some attributes in their responses.
More specifically, community endpoint misses the "shortDescription" attribute of the community while the collection endpoint misses the "copyrightText", "introductoryText", "shortDescription", "sidebarText" and "provenanceText". For the latter, I am not sure if we want to expose it to the public.
I do not know if this is on purpose, however, I have started a branch to track some changes which can be viewed here: https://github.com/kstamatis/DSpace/tree/dspace-rest-fixes
Should I find more information that is missing from the responses I will make the appropriate modifications to this branch before creating a PR.