Reimagining Healthcare, Education, and Government
I have been, and likely always will be interested and motivated to improve how institutions work. The three biggest institutions of our time that need to be reimagined are healthcare, education, and government. I don't think this is because healthcare, education, or government are inherently flawed or because the good folks working in those realms are foolish or stupid. Rather, I think those three areas are the last institutions to be reformed since the beginning of the information age because they're the biggest, gnarliest, and most difficult to change.
If you claim to be interested in "systemic change" and you're not working in healthcare, education, or government I'd seriously question your understanding of modern-day problems or your courage. These domains are where all the action is*.
* - It's worth noting that all these domains are inextricably linked to cities.