I think the F-Line function carriers will be able to handle the 7x17 I am making. I'm not sure how much bigger they can reasonably handle. They were only designed to support 8x10 (which is really a 10x10 back), but like everything ARCA they are very well made and can probably handle a bit more than their original design target.
Although I have three lenses that cover 12x20, at the present time, I have no plans to go bigger than 7x17. Of course, a year ago, I had no plans to go bigger than 4x10. So, you never know...