Ryan Welcher from 10up introduced SlotFill — “a modernized take on classic interface ‘hooks and filters' in WordPress” that extends Gutenberg's interface.
Slot and Fill are a pair of React components that allow developers to inject items into predefined spaces. Together they are “a pattern for component extensibility.”
Ryan shows how SlotFill allowed 10up “to maintain the classic editor UI conventions” for their Distributor plugin in Gutenberg.
Demo plugins are available, and SlotFill has been officially added to the next WordPress core release.