Since you have tagged this with things about elections and voting, I'll look at that general topic. I believe that an issue that will be very important is campaign finance.
After the Citizens United decision, we have seen the rise of "super PACs" that can accept donations of any size and use them to support candidates as long as they don't coordinate their strategy with the candidate. This allows people to give millions of dollars, literally, to support candidates. It will be very interesting to see how this affects the development of the country. Will these huge sums of money corrupt our system? Will it make people feel that the system is corrupt? If it does either of these things, what will happen to our system? This is a hugely important question that will face us in the years to come.