On the subject of the narrow time frame:
Having all the pre-production done is different than finalized rules. Having spent time laying out magazine/newspaper pages, you save a lot of time having the page layout done before actually inserting text. "Ready for the Printers" probably means the physical layout/ fluff stories are plugged in, and they just need to insert final rules/pictures.
On the subject of McMourning as a Guild Model:
It makes sense, even if he's on the run. I'm pretty sure if The Governor thinks you're of use to him, he's not giving a crap if you're Arcanist/Rezzer/Neverborn.
If I were to speculate on his list capabilities based on his crew box, then even in Guild he'd probably be allowed Resser models that don't have the Undead Characteristic (See Nurses/Sebastian/Rafkin) with certain exceptions.
On McMourning being an unnecessary beatstick:
Nobody knows how he's going to change, nor Lady J. Will Lady J be a brick house? Probably. Will mcMourning still slice n dice? Probably, but that might be something upgrades make him into rather than being one outright like Lady J probably will be.