Why don't YOU take the reference design, modify it, then get the boards made with a 'Textool socket'
Because I don't have the tools and knowledge to do that. I'm doing electronics on the stripboard level.
I assume you mean a ZIF socket
Yes, I mean a ZIF socket similar to this one:
Textool is a Chinese brand that makes thousands of connectors
Nope. According to the german wikipedia article about ZIF sockets, Textool is a brand name owned by the US company 3M. And AFAIK, they were the first ZIF sockets for DIL package. That's why I used it as synonym.
Though I see little to no reason to do this
Well, YOU see no reason to do this does not mean there is none.
My plan is to use the Uno as prototyping platform together with a breadboard.
After a project is completed, I'll take out the ATMega and put it on a stripboard together with the rest of the needed components. The Uno will then get a new ATMega for the next project. I don't think this is so uncommon.
Another use case:
Multiple projects using different shields, and one programmed (and labelled) ATMega for every project. Swap the shield, swap the ATMega, and ready to go.
I'm not able to spend 20 € + tax + shipping for a new Uno for every project. In that case, I'd rather buy china clones for 5 € (including shipping) each. The 5 € version uses the Mega16U2 as USB bridge, like the original. The ones with the CH340G are even cheaper. And on Linux, even those work very well without any driver issues.
I have bought two original Uno's and that's enough - until there is a new version with a new feature that's valuable for me.
My suggestion about selling a "Textool edition" was just an option to make it even more attractive to some people. See it as an opportunity for selling boards at a higher price. Then I would by another two of them. Of course, I would also be happy with just the "keep out area". Then I would also by two of them, desolder the sockets and solder the ZIF sockets.