For people wondering how the new Slate's Oliver Lefty carbon fork would work on the road, here are the pertinent details:

"Although suspension is a boon on the uneven surfaces for which the Slate is designed, it can be a disadvantage on smoother roads and when climbing as the up and down movement reduces pedalling efficiency, so there’s a lock-out on top of the fork for when it’s not needed."

Yup, as I suspected there's a lock-out! So you don't lose pedaling efficiency on pavement and can enable suspension for the rough stuff.