Considering, that this is just a single use case, it becomes very clear that this can only be done with sharding.
This is exactly what we are working on with IOTA.
I didn't have time to write the third part of the blog post, yet as we are currently focusing on getting the first coordinator-less testnet out.
There are still some open research questions regarding the exact parameters of such a system but it is the immediate focus after delivering on coordicide.
But this is of course just my personal "It would be cool to have a system to experiment with" kind of thinking and it might very well happen that it will take a bit longer.
Things like this are hard to predict.
What I really like about this use-case is that it shows where we are heading regarding a "decentralized future" of humanity and that it doesn't make sense to use VISA as ...
If we really think that DLT's are the future then we will need to be able to process millions of TPS globally and that is exactly what we are working on.