I suppose I can make summary after reading all this:
1. Any change in the development process will be possible if it will be convenient for each key developers personally only. (development process include build system)
2. Currently, almost all key developers use Unix like systems, they have strong old school C experience and current build system very comfortable for them.
I think new build system will be possible only by next reasons:
1. Autotools will be completely deprecated and unsupported.
2. Key developers will be changed by people with another experience and habits (and maybe younger).
I don't want to be CMake advocate here, and I see some problems with CMake to Postgres project too. But I want to make Postgres development more comfortable for people like me who also doesn't like mail lists and was growing with github. Unfortunately, we are too few here to change anything now.