Meeting the commitment given at Ignite 2018, Microsoft has published the preferred architecture for Exchange 2019. As you'd expect, the architecture is highly influenced by the cloud. The fingerprints of Exchange Online are all over the document, but at least it's nice to see some technology (the MetaCache) being transferred from the cloud to on-premises customers.
https://www.petri.com/microsoft-exchange-2019-preferred-architecture
