Recruitment within SH has been on-going now for a number of years this is nothing new.
Everything including bands is up for negotiation in the next EBA. I highly doubt you will see mass resignations.
The number 1 reason for the increase in recruitment is because the flying within SH has increased, we have natural attrition through people leaving plus VR, the company are doing the annual number crunch and sending perm crew onto LWOP, temp part time etc and as usual we do not have the crew to cover the flying program therefore the cheaper option of MAM are recruited. Nothing new, this happens every year.
As for the 747 if we are trained on the 747-300 wouldnt we also be able to operate the 400 as we currently do with other aircraft types?