Salva sis Calpurnia

It is an interesting suggestion, and not one without precedent. In the Mid Republic there were some instances reported by Livy where a consul's provincia was left open - by using a blank lot - for that very reason of awaiting events before assigning him as needed. It would be an even more pragmatic move in the Late Republic, where the assignments were allotted months before the consules would actually take office. There were other methods employed in the Mid Republic to create greater flexibility in assigning provinciae, but those may not have been available in the Late Republic.

Interestingly one of Caesar's "innovations" was to introduce the comparatio for praetores, when previously it had been reserved for consules. In a comparatio the Senate allowed the consules to collegially elect their assignments when uncertain circumstances left the usual assignment by lot unresponsive.