Even if we had fusion working already, a fusion powerplant would be expensive to build - comparable to a similar sized fission plant. At a conservative estimate

Even if we had fusion working already, a fusion powerplant would be expensive to build - comparable to a similar sized fission plant. At a conservative estimate of $2 Billion per GW, that $250B/yr would take more than a century just to build enough reactors to replace current fossil fuel consumption. Realistically, fusion is unlikely to be cost competitive with other power sources outside of niche applications. Even if fusion winds up powering our civilization in the future, something else will have to act as a stop-gap.