When I worked at the late, much-missed Ecomarine, we would still occasionally ship single boats to customers. It was always a pain to jump through the different carriers' packaging requirements, and sometimes impossible (one client wanted the boat shipped overseas, and the shipping company would basically have required a custom-built wooden crate for it.) Rotomoulded plastic boats were less problematic than composite kayaks, but we eventually stopped offering anything but in-store sales for all models.
That said, if you were doing this at scale, and had standardized prefab single-boat packaging that met the requirements of the most stringent carrier, and a staff who specialized in shipping, and knew the ins-and-outs of carriers and customs requirements, you might be able to make it economically viable.
So that would just leave the matters of build quality and flexibility on customization to be determined. Oh, yeah, and also fitting: while I sold a lot of Current Designs boats at Ecomarine and personally liked them, my mantra to customers was, "Fit trumps any features." I always encouraged them to at a minimum sit in a candidate boat, and if at all possible actually paddle it.
I remember that in the early days of internet shopping, one online electronics company advertised with the slogan "Our showrooms are everywhere" with the ad full of the logos of its bricks-and-mortar competitors. The idea being you'd check out the cool features of the TV or whatever in-person at their stores, then order the same product for less online.
Since Sanborne doesn't seem to plan any in-store presence for the CD line, where will their showrooms be? Tell people to find ads for used models of their boats on Facebook and waste the seller's time with a visit when they have no intention of buying? Because "free returns and we eat the shipping cost if it doesn't fit" might work for those slacks from Land's End that don't look as beguiling on you as they did on the model in the photo, but seems challenging for kayaks.
Or maybe they'll take a leaf out of Seaward's playbook. I don't know if this is still true, but back when I worked at Ecomarine, Seaward annoyed a lot of the BC local retailers who carried their brand by doing direct-to-consumer sales, complete with very aggressive pricing. So I had more than one customer I'd spend a lot of time with on Seaward boats, only to have them order directly from Seaward and pick up at the factory. So basically "showrooming" at the retailer. As a result, some retailers stopped stocking them even though they were (and, as far as I know, are) excellent boats. So one very effective way Seaward has always countered this, and marketed well, is with really competitive fleet pricing for tour operators and sweet, sweet prodeals for those in the industry (disclosure: the Tyee I own I got on just such a deal).
If you're newish to kayaking, and you show up for a multiday tour and wind up paddling a Seaward, and see that your guides are paddling pro models of the same brand, it's pretty natural to conclude that Seaward would be what you want when you come to buy your own boat. Perhaps Sanborne is planning something similar?