The possibility will certainly be there, but most likely it won't be optional in many places. Especially if atypical employment practices take off once again. There's already an example of this with a certain carrier from the Baltic countries whose contract allows for the company to unilaterally assign you up to 2 months of unpaid leave in each 12-month period. Not to mention that some other carriers have swiftly adopted the zero-hour contract concept and it might also be here to stay.