Interesting that they took this approach primarily for email referencing. Is it that common of a use case that it's worth changing the entire experience around it (and collapsing the formatting bar, etc.)? I'm assuming they tested some sort of referencing UI in the existing compose screen. Wish I could see that. Also, I'm wondering how image insertion works; modals upon modals can be pretty awkward for users.

My real pet peeve: can we start removing "Compose" from email vocabulary?