From what I've read, the current gen III reactors simply can't be built fast enough to replace fossil fuels in time, with low enough energy price. The construction time for a Gen III reactor is also easily delayed (our brand new reactor in Finland missed its promised delivery date by 14 years).
I have hope for gen IV reactors, but overall, the disconnect between how much hope people have on nuclear compared how much nuclear energy is actually possible to produce to the grid is huge.