Microsoft has issued a firmware update for Surface Pro 4 that provides better support for the 2017 Type Covers.
I’m traveling this week, so I can’t really test this, but, yes, Surface Pro 4 already works fine with the new Type Covers. This includes the Surface Pro Type Cover and the Alcantara-covered Surface Pro Signature Type Cover.
So it’s not clear what exactly this firmware update does, beyond the basics, as described on the Surface Pro 4 Update History site: Improve reliability and connectivity.
Anyway, you won’t see this update unless you are already using a Surface Pro 4 with a new, 2017-era Type Cover. But it’s already been added to the Surface Pro 4 Drivers and Firmware download set, which includes all current software, firmware, and drivers for the device in a single place.