worked fine with github: use a small script to sync online edits with github repository.
For (least priviledge) reasons it would be nice if the same could be done @ bitbucket:
Create a new key which only gets write access to https://bitbucket.org/vimcommunity/vim-git-wiki so that online changes can be pushed automatically.
Deployment keys get close: They allow to upload a key and associated it with one repository only. But you cannot push. Thus I recommend extending deployment keys adding an option allowing the user to choose between read only (current behaviour, should be default) and (rw, opt-in) - for some special use cases like mine
Of course I could create a new user and grant access to the repository. However I feel that's overkill.
I talked to Jesse Yowell (support) who suggested me creating a ticket (BBS-7401)