Yea, I also fear it'll disappoint gameplay wise. Hopefully they'll make up for the recent ones and make a step forwards on that aspect. I am also rather digging the classics, no matter how bad the graphics are for these days, they're still fun. It is mentioned that the scenes of that engine tech demo were rendered in real-time, therefore they actually could make it entirely look like that, but heavy hardware would be required obviously. Next gen consoles might be able to handle, but I still guess they'd reduce the graphics generally or just keep that level for cut-scenes.
Regardless of what the next FF is gonna look like, I guess this tech demo is a sweet preview of what technically can be done.