You can read between the lines here, and then the value proposition becomes much more clear for Facebook. For this to work, they'd basically need to provide a common engine for everything using the Metaverse. Rather than Second Life, people should be thinking Roblox as the closest existing technical implementation.
So, what's the value proposition in killing all existing 3D engines and completely replacing them? Obviously high if you can pull it off.
But this "metaverse" thing is really easy to write whitepapers and even fiction about it when you don't have to actually implement it, but gets a lot trickier in the implementation. For instance, right now, 3D engines are undergoing some pretty major changes in every release. This is not generally the time someone can swoop in and stabilize everyone on a particular engine for long periods of time, because while the "metaverse" is being written on this gen, Unreal Engine is advancing to the next level, and stuff written on that engine is going to be easier to write and look a lot better than the "meta" engine. There's actually some deep and fundamental reasons Roblox looks and plays the way it does.
There's other issues too; the "metaverse" envisions all this cross-platform avatar stuff, but are you going to play Call of Duty and its gritty "realistic" gameplay with 24 cartoony dufuses? No. Is Disney going to just happily license all of its characters to go into Call of Duty and get shot and bloodied? No. Are you going to be able to take your trademarked character everywhere with you? Exactly as well as you can stream whatever content you want from any content streamer today.
Building the technical platform is already a multi-billion dollar problem. There's a good chance it won't work well when it's done, but even if they overcome that, then they've got abundant legal barriers to overcome, in an environment where other companies are going to have every incentive to sue for their chunks of flesh.
I can also virtually guarantee that we're going to see very targeted demos, where the demos that Facebook puts out works well, because they were written in conjunction with the engine team, so the engine has exactly the features necessary to make the demo work, and nothing else. When EA goes to port Call of Duty into the metaverse, it's going to be a nightmare bug fest that looks like garbage compared to the real release.
When you think about the tech necessary to accomplish their goals, and then consider the social and industry implications of that tech, it's hard to see how to reach their lofty goals. The metaverse simply implies a level of cooperation and voluntary power ceding and a lowest-common-denominator environment that can't hold up the fictional portrayals driving the hype.
(I think ultimately it's a category error I've seen a lot. Fiction can be good at pointing the general direction the future may be, but taking fiction as a technical blueprint never works out well that I can see.)