It may intend to replace it [at some point] but it doesnt atm.

Why whould vb comply with something thats just a proposed recommendation ?
As far as I can tell from 5952, the whole "use lowercase" is just a 50/50 random choice based on the fact unix systems are case sensitive. Uppercase would be equally valid.
As long as your software (e.g. vBulletin) is consistant in its use of one or the other, it doesnt really matter which way you go.
Its all just preference really, I find lowercase looks really horrible & odd.