I think Soulweaver has us covered.
And while all this sounds like brilliant ideas, and while I would love to see this done, and I'd love to contribute, this project would most likely die. Especially with Project Carrot already looking promising. Perhaps try talking to Soulweaver about your ideas for this, maybe Project Carrot will support a new tileset format that allows double resolution.

Basically, though, I see what you're trying to do here, Dennis, and I fully support the attitude of getting things done that you're going for, but perhaps a full remake of JJ2 isn't the best way to go about it.