Indeed, the only difference between the v1.0 and v1.1 controllers that has come to light thus far is the control of the backlight; the earlier one is only capable of turning it on and off, while the newer board can set it to many different levels. If I understand correctly, this capability was intended all along, but, a problem was found at the last minute, so the v1.0 boards are restricted to on/off only, and the design was updated for the v1.1 boards. This is not just a matter of wanting the "latest and greatest", the fully dimmable version is suited for a variety of tasks that the earlier version is not (for instance, for continuous use in a room that is often occupied by people with dark-adapted eyes - say, a bedroom or "Home Theater" room).
Offering the v1.1 controller board separately would, indeed, be a niche item. But it has the positive aspect that there is zero development involved - it's an existing part (and I suspect it isn't manufactured in the same place as the actual LCD screen, which would mean they're already shipped around as plain boards) - take the existing board in its included anti-static bag, wrap some bubble wrap around it, and put it in an unadorned cardboard box with a plain mailing-label style sticker that simply states "v1.1 controller board for Raspberry Pi 7" display".
As W. H. Heydt suggests, start with a very small quantity. Put 100 (or 50 or 25) on a shelf, add it to the webstore, and announce (here, or here and on the main blog) that it is available. Charge a price that covers ALL the expenses involved in the board, packaging, shipping, and additional logistics for having it be a "one-off" thing (including a charge to cover the potential costs of closing down this side project if it doesn't go anywhere). Mark the purchase page clearly as "no returns except for actual physically defective boards", and "no new documentation provided, don't buy this if you don't know what you are doing". If the first batch sells, allocate some more. If none sell after the first few in the first month, then send the remainder back to the factory, so they can be packaged into the official display kits as originally intended. I don't want there to be any net/uncovered cost for the foundation, I'd just like to be able to equip my second display with full dimming capability (sure, I could buy a whole additional display, but I'd always have a non-dimmable one around - I'd _much_ rather end up with a "spare" v1.0 controller board on my shelf, after swapping in the new one). I'm betting that more than a handful of others would cheerfully buy the boards as well.