I’ve never once nailed the timing, but I have two predictions.
The first is William Baumol, who is I believe ninety-four years old. His cost-disease hypothesis is very important for understanding the productivity slowdown, see this recent empirical update. Oddly, the hypothesis is most likely false for the sector where Baumol pushed it hardest — music and the arts.
The other option is a joint prize for environmental economics, perhaps to William Nordhaus, Partha Dasgupta, and Martin Weitzman. A prize in that direction is long overdue.
The “Web of Science” predicts Lazear, Blanchard, or Marc Melitz, based on citation counts. Other reasonable possibilities include Robert Barro, Paul Romer, Banerjee and Duflo and Kremer (joint?), David Hendry, Diamond and Dybvig, and Bernanke, Woodford, and Svensson, arguably joint. I still am of the opinion that Martin Feldstein is deserving, don’t forget he did empirical public finance, was a pioneer in health care economics, and built the NBER. For a dark horse pick, how about Joseph Newhouse (RCTs and the Rand health care study)?
There are other options — what is your prediction?