It should be possible to make a dumb version of such a keyboard wired the same as the stock one, just with the keys moved around. It would need some OS configuration to be truly useful, though.
Similar to a sibling comment, and perhaps not really applicable (since this isn't a company making something people can buy...), but the MNT Reform is amenable to fitting a custom/ergonomic keyboard also (I hadn't seen the Framework in the sibling comment, it looks very cool!).
I don't know how to link to it directly, but midway down this article there's a picture and some more links of an MNT Reform (apparently completely home-built) with a very cool, "thumb-centric", column staggered ergo keyboard:
I actually like short travel very light linear switches, mechanical or not.
I don’t like row stagger and non-split keyboards, for ergonomic reasons. That’s definitely a niche preference, but if anyone would cater to it you’d expect it to be Framework or similar.
You're right that Framework is exactly where I would expect flexibility on this: I mean, just looking at their landing page - you see a laptop without the keyboard and ports. Framework offers 176 (!) kinds of "keyboards":
(Answer: it's basically just keyboard covers, and the many options are due to variations of colors and languages. But I would take a hot pink / toxic green keyboard with ancient tibetan labels if the keys were non-chicklet, with decent travel, sizes, and feedback. 7 rows if possible.)
Overhead of small volume manufacturing. If they make all those variations and intend to continue existing as a company that makes money selling things, it would have to be at a price where no one's going to buy one. But if I start an Etsy store selling one-offs at $399 each, people can grumble about my price, but it's not on Framework.