I didn't say Expedition. Expedition is on the Superduty chassis, not the F-150.
You said "the F-150 SUV", and the Expedition is the SUV which has always been on the same platform as the F-150 (although sometimes lagging in generation, and in recent generations with IRS). The
Expedition was never SuperDuty - the SuperDuty-based SUV was the
Excursion. The "E" names can make it difficult to keep the Ford SUVs (including the Explorer, Escape, and Edge) all straight, and "Expedition" and "Excursion" are particularly close.
Yes, it would probably be technically easy for Ford (or even a DIY builder) to put an SUV body (which is the Expedition) on the Lightning chassis... if that chassis were short enough, and it's not. Unlike an ICE pickup, the frame cannot be easily made shorter, because the battery fills the available length, instead of having relatively empty space.
The old
Expedition SVT Thunder using some parts usually available only the F-150 was a minor variation of the regular Expedition, as the Expedition was then (as always) on the F-150 platform.