When you say 'crews' do you mean flight deck or cabin crews?

I don't think it would be a worthy option if it was for flight deck crews. Unless they had previous endorsements on B777 aircraft. I know for a fact a lot a A380 crews trained up on the A330/A340 type aircraft and then when the time came (seniority level) were transferred onto the A380 or even the B777.

Emirates are currently operating 20/21 Airbus A380s, with A6-EDK still out of service.