I dig this old thread for a recent change in the plates:
Now custom plates do not have to begin by a "9-".
You can chose what you want, up to 8 characters. Letters & numbers must be separated from each other by a dash, which also counts in the number of characters (in this way current plates count as 9 characters: you can't make a custom plate that looks like one from a regular series).
It will still cost 1000 €.
Those who already bought a "9-" custom plate can drop the "9-" for 30 €.
Numbers-only plates are still forbidden (royal plates), except for old-timers from before 1954.
Of course they will restrict the words that you can put on these (racist, political, insulting, ...)

And about royal plates, a fun fact:
http://www.7sur7.be/7s7/fr/1502/Belgique/article/detail/1823806/2014/03/20/Le-Palais-voit-defiler-les-PV-adresses-au-Roi.dhtml
For those who do not understand French, the king was getting a lot of fines, mostly speeding tickets. And all from France.
It appears that there was a bug in the French system for the new plates starting by "1-"... so they dropped all what was after the 1 (and "1" is the king's plate).
I wonder how they didn't notice that sooner