Finally the patch has been submitted as bug/enhancement #10919. As said on my previous post there was a little issue with importing the variable saved in the ports.conf file. Thanks to Philip the problem is solved. For techies: I defined my variable as

portarchivebinhost   "http://mac.vandeplas.com/packages"

instead of

portarchivebinhost   http://mac.vandeplas.com/packages

(without the "). It was as simple as that...

The next step is to work on a chroot where I can safely compile the ports without filling my system with unwanted things (that's what I was doing now, and it looks like that MacPorts doesn't keep a list of the installed files like gentoo/portage does).

On the other hand I will need to work on my script to automagically compile all ports with different variants. That is a little more complicated as it looks, because some variants should not be used together. I'd be also nice to keep a list of the ports that do not compile cleanly.

That's all for my 3rd bugreport for MacPorts.