I was never able to find an ANSI/ISO standard for this size, going back to the 1951 version.
Originally Posted by Rob Skeoch
Given their price, I don't think the Lotus holders will take hold as a "standard." It will likely come down to them or the impending Fotoman Camera 6.5x8.5 holders. While an exact weight is not yet available from Fotoman, I suspect those will be noticeably heavier than Lotus', considering Paul is using high density plastic as well as metal septums and dark slides.
If one were designing a camera back, I'd suggest sizing for the Lotus holders. That would permit using either them or the very slightly smaller (outer dimensions) Fotoman holders, with the choice based on criticality of weight and budget.