Don't know if this has been mentioned before or if it is already possible, but in some cases it could be useful to add your own example sentences to definitions, for instance, when I find a new word in a context, I'd love to record the first time I saw that word in that context because that's often the best way to remember these words. I can understand that adding a sentence to entries in GF or other dictionaries would seem a little odd, so maybe marking them with some icon to let you know it is not an official one could solve the problem.
Also, sometimes adding definitions would be great. Being able to have the option to share these with the community would be great too.