They went with 28nm because it was the last planar (aka cheap) node around. GlobalFoundries recently launched their 22nm planar (22FDX), so it seems like there's now a cheap path forward for making a new chip with an updated CPU design (and hopefully an updated GPU too).

I can answer the question posed in that thread: Because the performance would be abysmal. The Raspberry Pi is a neat device for $35, but even running native ARM code it sometimes struggles to provide a good desktop user experience by 2022 standards.

The major use-case I can think of for building a rosetta-like x86 translation layer for the Pi is to run Windows software. All the relevant Linux software can, or has been, ported to ARM. Do you think the average user of Windows software is going to be happy with the performance of an x86 emulator running on a $35 ARM computer with barely enough memory to run a few Chrome tabs?