That's what they said about regular electric grid power too - that it "soon" would be so cheap as to be unmetered. That was half a century ago and it didn't pan out...
The reasons for this are entirely political. Technology, left to its own devices, would have followed the usual maturity curve on fission power, which would be universal, ubiquitous, abundant, and cheap.
Solar power has neither the geopolitical problems nor the squishy 'environmentalist' ick factor of fission. There's no reason not to expect another halving or two of PPP dollar per Watt to follow.
