So, only 33 month later I can report the outcome of my efforts with my bricked N9/16GB.

Perhaps for future visitors which are interested in this topic (more and more unlikely as time goes by), but mainly to give the guys an update who helped a lot (hopefully you are still subscribed to this thread).

Cut a long story short: I was able to rescue my phone and also my data

But much less spectacular than you might think:

After digging through the schematic and the layout to find the serial rx/tx port (my thought-so last resort), I though it would be a good idea to fresh up my memory how the phone behaves when booted via the flasher. So, I tried to boot the bare mainboard via the flasher (under Debiab GNU/Linux 8.2 (jessie)):

(This could be, but must not be the command I used before, because I didn't documented it back then)

And, just by accident the volumes of my phone popped up after some time! Just for a few seconds, but reproducible after a reboot, so that was enough to rescue the important files I was after and to fix the issue with ~/.profile.

I put the mainboard back in its case and my thought-dead N9/16GB was back to life again. No problems what-so-ever! Either it was some self-healing over the years (that's my favorite guess ), I did something wrong with the flasher back then because I had blinders on or some kernel update on my computer helped. I don't know.

So, the lesson is clear:

- the MALF kernel works also on the Nokia N9 with only 16GB
- and most important: Don't ever mess with the .profile file!

Thanks to those who answerd my questions patiently, especially juiceme