I think V wasnt a bad choice of letter considering its the only letter with any appeal that hasnt already been used, but the confusion with engine configurations. Imagine the new audi V4
V4 Owner: Hey I've just bought a new Audi V4!
Friend: So you've bought bought an Audi powered by a 4-cylinder engine, but not one arranged inline like almost all 4 bangers
but in a vee shape?
V4 Owner: Nope

Friend: Hmmmm... let me quess an efficiency or sport orientated A4?
Owner: Ummm no?

Friend: A rival to BMW's much anticipated 3er GT??
Owner: No!

Friend: Then what the hell is it??
Owner: An MPV

Friend: Oooo. I see. That must be nice. ( Then walks away, coughing in a vain to attempt to disquise the laughter that came close to overpowering him) P.S The owners erection subsequently waned when he realised he'd spent the family inheritance on a posh ( next-gen) Sharan.
Heres a quick list of the letters that are already in use to be combined with a single number.
A Audi
B Alpina
C Citroen
D Alpina
E Used on precursor to "i" Cars for concept E1
F Mclaren
H Hummer
i BMW
K Kia
L Used by BMW for L7 (Limo E38 Series: Only for certain markets)
M BMW
Q Audi
R Audi
S Audi
T Used by Caparo for T1 supercar
V ....
X BMW
Z BMW