At this point I think it's perfectly fair to start with the assumption that a new Crypto is a scam and it needs to do the legwork to show that it isn't. To claim that a blockchain (the most ludicrously inefficient data-structure ever devised) can scale to a billion users is an outrageous claim. The technical means they found overcome this problem should be front and center in their documentation.
The question becomes: what is tx throughput at N billion users? What are the scaling strategies that will get us there? It is zk-rollups (or zk-zk rollups)? Is it sharding? Is it moving to custom hardware circuits? I suspect it will be some combination of all of the above.
We don't know what the answer is yet and we will devote tremendous resources to figuring it out. I don't want to give the impression that MobileCoin as it is written today will scale to Alipay levels of tx throughput, but I do believe there is a path to get there that requires a ton of work.
Does that answer your question?
Presumably you've come across this question in your four years of development and would have exact numbers (perhaps not for my chosen value of tx/sec) already at hand. The fact that we're three comments deep into this, leads me to believe you are dancing around the question.