Where did 400 come from?
I pulled from my extravagant arse, with not even enough analysis to fill the back of a beer coaster.
But, since 737 average utilisation is less than 220 hrs month, even five crews per plane is probably stretching it. So assume around 160 surplus there by any rational measure of eficient utilisation. (Not by cost though as their min divisor is so low. )
We must be under 100 surplus on the international side, and if the 250 number on LWOP is correct, then you get over 400. Which is enough to crew twenty 787s. Or one standing out in front of every Flight Centre in the country.
Anyway, at least we are all getting new brand enhancing uniforms. I do hope it has a sash, and a lanyard. If you are going to enhance the brand it calls for more than half measures, after all.