The preconnect relationship is intriguing; I hadn't been following the adoption of resource hints.

Sidenote: I find it really interesting that the current spec suggests preconnect and its siblings accept a probability attribute estimating how likely connecting to different resources is.[1] Something funny to me about making the directed-graph/state-machine nature of the internet finally show through the markup.

[1] http://www.w3.org/TR/resource-hints/#hint-probability