Copying postfix to the RAM rootfs is normally not the nice TC way 
Not to argue with your decision on how to implement your extension i think for the scope of it your decision is right, but i would argue that copying postfix to RAM fs is not a nice TC way. I think the recommendations is meant for PC/NC like implementations (fast boot, ~dynamic extensions, ~slow access) but the feature is perfect for small single purpose servers (~slow boot, ~static extensions, fast access) and i beleave the features is also very much within the scope of TCL's main usages.
I actualy more see mounting squasedfs to loop devices as a hack way to make it fit for PC/NC usage and "copy to fs" to be the real/nice way

Anyway good work thanks, keep it up

-- Regards Andreas