Just note that design isn't an algorithm and it evolves over time one way or another. Therefore in addition you will likely need to figure out (over time) where the evolving phase should be going on. I will leave that part to you and FreeCAD community and other contributors to push you in the correct direction over time. I was thinking currently there is no program available for contributing single commands to FreeCAD. Some sort of staging area for commands. If something like that will be achieved in the future maybe that place can be used for upstream design playground purposes. And obviously icon packs will hopefully have strong influence on usptream design process and guidelines in the future.
Note that all in all i am happy with the current situation. There is dedicated forum section, there is prolific and critically acclaimed work going on in all the mentioned areas. Looking back i can only remember two things you the new generation of design contributors might want to tackle when searching for new challenges:
And i said in the past for whoever will deserve it should have a shot at FreeCAD logo. For FreeCAD 0.17 therefore my proposal would be for you @agryson and for @pablogil to try to tackle it together. I see it for @pablogil to do the hammering and for you to to do a paint work. If you are interested ask him if he is interested. You two take the time and figure out the details and i only have one request. Don't make me look bad for proposing this if you two decide to do it.
Beyond that if all that will be achieved likely you the new generation of design contributors will need to figure out where to take the ship next for yourself. It will likely be challenging at times but you'll make it just fine.