No idea.
When they switched letters & numbers, they changed a little the typeface (characters seem a little bolder) but kept the old narrow format.
It is nearly as narrow as US plates, allowing to put it on US-specs cars (borders have to be a little folded sometimes). I guess it is an advantage even if these cars are not very common. EU-plate would not add much. I would not like to lose our red+white colors for plates, but I am not against a EU-sized plate with euroband if Europe requires it some day.
Note that EU-format plates are already used for dealer plates (green on white, starting by Z) and trailer plates (black on white, starting by U or Q).
As front plates are made by the car owner (only rear plate is delivered by the state authorities), lots of cars have a EU-format plate on front.