Fantastic video for someone just discovering cross-blockchain protocols - I went to a Berkeley meetup and they talked at length about Tendermint and mentioned Cosmos, the Ethermint "hard spoon - a friendly fork" (gotta love nerd humor) so fortunately I understood pretty much everything you talked about.

A question about Cosmos - so if there are multiple Cosmos Hubs being operated are they actually separate, or because as you say Cosmos Hub itself is a blockchain can they all talk to each other using the same cross-blockchain protocol? Then we end up with a mesh of hubs?

I really like the features of Polkadot that reward full node collators and the fishermen. As for exchanging data between chains - I feel like that is less important if you use a separate chain itself like IPFS or even a blockchain database like Bluzelle to share data. I haven't looked at how Polkadot stores/moves data but it seems like anything but trivial amounts shouldn't really be on the chain itself. I guess only time will tell...