Once again thanks for the detailed reply Marcin!
I had a look at LifeSaver and its counterpart pioSaver, unfortunately Lifesaver won't work for Cryptomatte as it only saves out to multi-part EXR's and neither option saves in the cryptomatte metadata.
Unless I've missed a step, for now we may still be stuck with creating two renders (beauty elements vs. masking/utility elements) but being able to re-order the render into multi-part will no doubt be a huge help, especially with the smaller sizes DWAB brings