Nuclear should be considered part of clean energy standard, White House says

The biggest problem with fission power is up front capital cost. It takes so long to pay off the mortgage that, by the time a nuclear plant pulls ahead over a fossil fuel plant, whoever decided to build that plant is probably getting ready to retire.

We have every reason to believe that a fusion power plant will be even more expensive and slower to construct than a fission one. So, even if you skipped over the additional expensive and slow step of proving that a reactor design works, they still wouldn't be chosen by any energy company that expects to turn a profit.