The most well known thing about Musk besides being an asshat, is that his timelines are almost always imaginary. He is not building fabs on the Moon in "just a few years".
He doesn't have to build them to sell them. FSD has been sold for almost a decade, more than half the depreciation time of the cars. With first principles sales techniques it's possible X could sell these moon chips now and deliver them made on earth 6 or 7 Moore's law cycles later by a different company, like with the solar roof or hydraulic brick machine from alibaba, way cheaper.
But how is that at all related to the DRAM manufacturers' short term production limitations? Unless I'm being dumb and you're saying that these manufacturers could also just kick the can down the road for a few fab generations?