If you have the ability and time, I would focus on AI software and robotics to provide healthcare. I heard a quote on Bloomberg saying that we will be losing a million doctors by 2020. The cause? I didn't catch that part, but my guess is retirement or because the field is no longer viable between the high malpractice insurance premiums and low reimbursement rates. The coming generations will have less access to doctors at a time when they need them the most. That's an amazing opportunity for those who can deliver healthcare at scale and at an affordable price.
The trend since the 1970s in which the wealthiest reap the majority of any economic growth and hold more and more assets while the middle class and poor have seen wages stagnate as compared to inflation or shrink, and an increasing gap in wealth. http://www.cbpp.org/research/poverty-and-inequality/a-guide-...
The trend of finance as an increasing part of GDP and shareholder return being seen as a better proxy for economic success then long term growth, investment in durable assets, and infrastructure, especiall when much of the value finance and immediate shareholder returns add are questionable. http://www.washingtonmonthly.com/magazine/novemberdecember_2...
For the human race: Safe water, war, climate change, and better access to space are probably on the list. The insane US political climate might be up there, too.
For us on HN: Anything that you can do to make a dent in any of the above problems. Also, internet security is completely broken and needs a total re-think and re-do. We need safe access to the world's information for the several billion people who are not yet online. (For that matter, we need safe access for everyone else, too.)
Edit: also, reasons for why listed problems are in higher priority than others (in your opinion), and potential solutions would be very interesting to read.
Off the top of my head, this might look like:
Cement block housing, very limited plumbing (with ability to have a pitcher pump at the sink), composting toilet, some kind of simple fold-out cot/bed/hammock, small furnace/woodstove?, etc.
Make housing so simple & affordable that every single person can have a safe place to stay, even if that place is without luxury.