Omnibus as bus is really dated, today it´s used by the techie people to mean a combination of equipments that will act as one at the very last. As in modules, for example. Anyway, the parts has a separate function per se.
Here a simple use of the concept:http://www.afcindustries.com/omnibus-multi-level-desk-d40
Other meaning, is that of "whole" (integral/coletivo(a)) as in "omnibus accounts" or "ommibus bill", etc. That doesn´t mean that one can´t find the word used as bus/vehicle, mainly in older writings (and even in more comtemporary ones - but then used for effect.)