There is work underway pursuing GB sized blocks (https://themerkle.com/what-is-the-gigablock-testnet-initiati...). I think it is a feasible path forward. And even if it turns out to be difficult to achieve with today's infrastructure and technology, cryptocurrencies won't suddenly have a billion people using it for daily transactions overnight. I think we could easily support 100 MB blocks now - which would be 100x what current bitcoin provides. In my opinion, that provides quite a bit of time to continue to investigate various scaling avenues.