Somebody _is_ kind of doing that: https://geoff.greer.fm/2017/07/16/thinkpad-x62/ . They also mod x220s but the mod is more invasive since they require a different screen bezel.
I recently got an x62 and it's great, although you must put some effort into making linux work smoothly on it and making the screen brighter. But all in all I am extremely happy with it.
Most of my work happens over SSH, my laptop is currently fast enough for Netflix, email, and web browsing. I'm capped at 2 1920x1080 monitors but this is livable.
I think if someone took the old X220 generation Thinkpads, upgraded the internals, and kept the keyboard and docking that they would sell like hotcakes.