sharding is in the same boat as proof-of-stake, nobody knows if a system can be built that preserves the level of security of current monolithic and proof-of-work systems, it is being studied on an academic an implementation level by several teams including Cardano, ethereum and ethereum classic.

On the scalability issue if you sacrifice the decentralization is theoretically possible for Bitcoin to process on-chain, Visa level of transactions and with current energy consumption levels or even less.

You would probably get 3 to 6 physical data center locations probably on the same continent connected with high-speed links with 1 Terabyte 10min blocks.