I suppose they could solve superintelligence and cure cancer and build fusion reactors with it, but that's 100% outside their comfort zone - if they manage to build synthethic conversation partners and synthethic content generators as good or better than the real thing the value of having every other human on the planet registered to one of their social network goes to zero.
Which is impossible anyway - I facebook to maintain real human connections and keep up with people who I care about, not to consume infinite content.
if OpenAI can build a "social" network of completely generated content, that can kill Meta. Even today I venture to guess that most of the engagements in their platforms is not driven by real friends, so an AI driven platform won't be too different, or it might make content generation be so easy as to make your friends engage again.
Apart from it the ludicrous vision of the metaverse seems much more plausible with highly realistic world models