Achieving practical nuclear fusion for power generation would be a very nice step forward. But "holy grail" is rather overselling it, I suspect.
Even when practical, we're still talking very big, very expensive plants that depend on a long supply chain for all its parts, the high-purity fuel and so on. When you consider the building, running and maintenance costs, and the cost of dealing with the spent fuel (much better than for fission plants of course) the energy won't be all that cheap. Hopefully cheaper than fossil fuels at least, but I would not be surprised if a first generation of plants, at least, become more expensive than that.
And they'll be competing with rapidly dropping costs for solar and other renewables. A big, expensive plant like that will need a 40-50 year lifetime to pay for itself. If you can't show that it will likely run profitably for that time period few or no companies will be willing to take on the very major investment. We may well see a technical breakthrough for fusion, and still get no plants actually built.