Chances of pulling it off eventually are very high - I started my PhD with naive prior of around 0.5, and I'm converging on something like 0.9 now.
The hardest thing is discovering how the system is fundamentally regulated, and we are making rapid progress. Our massively high throughput approach gives us huge lists of candidate genes with probabilities, so we can rank them and process them through a biological testing pipeline quite fast. Using this process we've discovered a whole lot in the last two years - for example we now have a toolbox of genes we can use to precisely time gene expression in the bundle sheath cell (the cell C4 plants concentrate RuBisCO in). Our computational systems are rapidly improving, and I think 2015 will be a big year for us. Final year of my PhD, and I intend to go out with a bang :).
The secondary challenge is building the system in rice, but unless everything we know about molecular biology is wrong, this will work. We've already started by putting the parts we do know about in the right places in separate plants, then breeding them together ('gene stacking'). This happens in parallel with the discovery.
The major uncertainty is in the timescale - 15 years is ambitious, but not unlikely. 20 years is likely. With a colleague at LSE, I did some simulations of what the impact of success would be at various timescales, and 20 years would still be a vast humanitarian win. Every year we can shave off the time to delivery potentially saves tens of thousands of lives and lifts another hundreds thousand or so people out of food scarcity.
The first two stages of the project have proceeded in parallel, so we've been doing gene discovery and stacking in rice at the same time. I think we're probably 3 years behind schedule - the gene discovery part of that original pyramid is very optimistic.
