maybe hponcfg could also used to determine these informations

Hmm, it should already happens:
glpi-agent/lib/GLPI/Agent/Task/Inventory/Generic/Ipmi/Lan.pm at develop · glpi-project/glpi-agent

And maybe also create the ipmi interface (including mac) within network interfaces

Especially Business Network Equipment using and needing licenses. 

Is implemented ;)

Or LibreNMS

What about the integration of Observium?

That somehow sounds like another question of me:

https://t.me/glpien/4241

Not exactly the same.

Example:

Switchport XY is attached to networkoutlet Z and device Y. Network outlet Z is located in Location D ... so location of device Y should be set automatically to D.

Finally I figured out, that it is already possible to transfer locations between entities. First the entity has to be select, than "transfer and merge" move the location to the specific entity.