Sean Ong says the same in his latest video where he tests the SP4 battery life. The SP4 has the connectors to support a power cover but for some reason it doesn't work! Maybe MS plan to release a new power cover?
My crazy fantasy is one day MS would bring a base keyboard (simillar to SB) out with dGPU, extra battery, more ports, etc, as an optional upgrade for the SP lines. Even cooler, if the base could be upgraded with additional ram, storage newer dGPU.
Then you could upgrade SP line over time (2 or 3 versions) and reuse the base along the way. Converge SP and SB and make the virtual bezel rumor, prior to launch, become a reality. Gotta be in future pipeline.