I would have hoped that the previous threads and bug reports about this would have made it clear what the issue is here.
Something/someone has chosen/selected/set a system GTK2 theme that includes color definitions (specifically what GTK calls a color theme).
There is a bug in GTK2 (which will never be fixed) which causes it to hang if it loads two themes. Ardour is one of the few applications which defines its own color theme. If there is no color theme in the system GTK theme, no problem. If there is, then Ardour (and any other application that defines its own color theme) will hang at startup.
You need to set GTK2_RC_FILES=/dev/null in your environment to prevent GTK from ever loading the system-defined theme. How best to do this depends a lot on your specific system configuration.
Alternately, you need to change the system GTK theme to one without a color specification.