Does anyone on the team can give me a straight answer?
GSX already supports different kind of buses depending on airplane size, down to a very small 6-seat model so, it can accomodate most of the usual cases. No, we don't have a limousine right now, but it's surely something that might be added, even if it's not really an high priority right now, considering we already have several variations of bus sizes, while GSX is still missing entirely new services (like de-icing, water, cleaning, etc.).
As explained many times already on the forum, these will come before anything else, then we'll probably have another update to the scenery editor, then we'll likely add support for loading baggage from the left side of the airplane and THEN, we might start digging into such smaller nice-to-have-not-indispensable features.
I'd say that limousine would make more sense when we'll eventually have visible passengers, which is the top-most requested feature, we know that, but it's also the most complex which will require going into research mode again.