There is nothing wrong with some branches having "detached head". You will see this when there has been a recent update to our 1.3 development branch.
If you see this at the end:
Sync successful and kits in alignment! :)
Then it means things are OK.
OK, I 've set to python3.6 via
root@carbon nik # eselect python list
Available Python interpreters, in order of preference:
[1] python3.4
[2] python2.7
[3] python3.6 (fallback)
[4] python3.5 (fallback)
root@carbon nik # eselect python set 3
root@carbon nik # eselect python show
python3.6
and it worked. Thank you for the hints!