Hello,
Firstly, I know that Debian 9 will be ready when it will be ready. But I'm looking for more details about, e.g. Gnome's version, etc.

Official website links to https://wiki.debian.org/NewInStretch, that shows 404 error.

The NewInJessie has a lot "work in progress", when Jessie is already released. For me those pages are just abandoned.

Are there any mailing lists, wikis, etc., that shows current progress in Debian 9 development?

Are there any blueprints for Debian 9, planned Gnome's version? 3.16 or something higher? New packages? Some major changes? Planned kernel's version?

I've made some bugreports in Debian's bugtracker and I'm disappointed, that a lot of them stays open for months, when in CentOS (or better, RH) explain bugs and fix them much faster.

What's going on?

It will be out in ~2017, so it is very very early to guess what will it contain. My guess is
- xfce 4.12, because xfce has really slow release schedule
- gnome 3.20 or something near it
- kde 5.x because it already begin in unstable