Just an update....
After a very long struggle with this issue, i was able to manually repoint the VCSA5.5 to a new PSC 6.0 Appliance, despite having someone at VMware saying it was not possible.
The repoint operation is very complicated and it took me 2 months (may/june 2018) to clean up this environment, without losing the consistency of the inventory database, nor the vcloud environment.
After that, the upgrade was successfull.
I am now running VCSA6.0 with external PSC, but will upgrade to 6.5 with embedded PSC.