Kernel 4.9 - a warning especially to KDE users

[Yoogle]

Till a few days ago I'd installed a Sparky 4.5 system on one of my four hard disks as the very best system of several edge distros I'm currently testing. For I just wanted to have a newer 4.8 kernel I'd enabled Sparky's unstable repo. Unfortunately one of the last global updates brought with it that fatal jump to 4.9.
My workstation is is based on an ASUS Sabertooth 990FX (Ist gen.) with a FX6300 and a Radeon 260X graphics card, and I always strongly prefer KDE Plasma over any other desktop environment. Only in "case of emergency" I'd accept Xfce as the only alternative.
First, there are some cryptic warnings at bootup announcing that one certain firmware version could not be used and had to be replaced by another. Finished login, some tools no more worked. Especially Ksysguard on kernel 4.9 isn't able to show any graphs of resource usage. And when doing a fallback reboot with any older kernel that failure will persist, so an update to kernel 4.9 means there's no way back.
Before I told you that simultaneously with Sparky I test other distros, also on KDE: It's the same problem with Fedora Rawhide and openSUSE Leap (the latter one with special kernel repo enabled)!
I'am not expert enough to find out where the bug is located. Is it a kernel-near or a systemd malfunction or does it have to do with the CPU's or the GPU's firmware (respectively with them all not yet been well harmonized)?
Be it as it is - better stay with kernel 4.8 (all subversions working excellently!) and wait some time for further kernel development ...