120" does sound too ambitious as there doesn't exist a single TV panel of that size(the MicroLED offerings are multiple panels), but it certainly would make life for home theatre projectors much harder with likely double the maximum brightness of a ~$30,000 flagship while providing a comparable black floor, not to mention far better light rejection, and easier setup/calibration, only at a likely cost of color gamut.
86" OTOH would break no record and existing 85-88" LED TVs from budget brands already have an accessible price, so even if they could make it cheaper it's not that big of a deal.