This would definitely be of interest to me. I think I'd prefer a single piece to a two-piece T-Top.
Ideally, this would also store behind the seats, which might shift the seal points so that it would fit between the B-pillars. I imagine this having a very simple single manual clasp mechanism...
A major appeal of the Slate is that it's a small 2-door pickup - never mind that it's electric or modular. 4-door pickups are effectively lifted sedans without a trunk lid.