This is a two-minute, 30-second video said to be of a tech demonstration of "Fortress," the Final Fantasy project GRIN was said to have been working on when the Swedish studio closed.
Few details accompany the video, whose visuals and action-oriented gameplay are very Western-oriented, to say the least. The video's action sequences are broken up by concept art from GRIN that we've seen before. The only detail recognisably familiar to me, and I'm no Final Fantasy expert, is the chocobo around 1:20.
The host of this video (whose YouTube profile, by the way, identifies him as "William Mark Felt"), says the game is "set some time after the events of Final Fantasy XII: Revenant Wings," and is meant for the PlayStation 3, Xbox 360 and PC. "The project has not been officially announced yet, but its existence is known due to information leaked by former members of the development team and sources in the video game industry," the host said.
"The Fortress project is still supported by Square Enix and in development at a currently undisclosed studio - possibly Eidos Montreal, Square Enix's main Western branch," he said. No sources for that information were cited, although earlier reports said the project was still in development.
I have emailed a Square-Enix representative to ask if the company has any comment on this video. If any is offered it will be updated here.
FFXII Sequel - FORTRESS - Tech Demo Footage [YouTube]