Unfortunately large fusion is unlikely to ever be economic because the cost of solar/battery is coming down so quickly and is already in the 1-2 cents per kilowatt hour for the solar component. And costs will continue to drop.
Small scale fusion on the other hand would have a viable niche application at the poles, in the sea or underground or any other environment that is without sun or space.
We won't know what the cost of solar/battery will be in a sustainable energy economy, until someone builds a solar-powered solar panel and battery factory. At the moment, productions costs are heavily (as in, entirely) subsidised by fossil fuels (mostly coal).
