Yeah, I think it will be original. Just like how I feel like every expansion before it was original.

Every FF expansion clearly takes some notes from a previous Final Fantasy in what sort of story it wants to tell and how to tell it, while then actually telling its own story in that same space; Heavensward is the hardest to read but it's sort of 'VII in different clothes', Stormblood is clearly riffing on VI and XII. Shadowbringers took notes from X and VII (Eulmore's a Midgar), while pretending it was taking notes from I. Endwalker is a little hard to read due to the famous expansion mashup, but I definitely read it as pulling from IV (even excluding the patch content), with some veins from VI, II, and possibly XV. And Dawntrail was obviously going for IX with a bit of X mostly as, like, connective tissue, but was doing IX in more complex ways than people give credit for; most people just saw the obvious markers like Alexandria and Sphene and kinda stopped there.

My gut feel for 8.0 (outside of 'I don't care yet, let me keep liking Dawntrail') is to either count VII out entirely, or to expect it to be sort of the 'fake inspiration', like 1 was to Shadowbringers; maybe the collectors' edition rewards are VII themed and we have something similar to how Stormblood's were V-themed despite the expansion very much not. I honestly think they've played the VII notes too often, and doing a 'VII Expansion' in the same way that Dawntrail is the 'IX Expansion' would mostly seem unoriginal; not only is VII a fairly 'active' corner of the property right now, but they've borrowed from VII so often before that it's just gonna feel like we've done all this before.

I think the next one going in on X would be a safe and strong bet, but I think VIII is an interesting vein they haven't done much with before, and I wouldn't be surprised to see that one take the lead. Or go absolutely wild and we hit, like, Type-0.