I need to split a package while switching off unpacking for some of the subpackages

[msdobrescu]

The purpose is to build once and to generate several subpackages out of it.
This saves time and power.

Is your feature request related to a problem? Please describe.

It took a while to experiment and figure out what happens.
Basically, I've tried to build once and get a MocaccinoOS set of three packages out of one specification, a buildbase, a regular enduser package and a package that contains the same end user package contents and the portage meta-data files.
A package split in subpackages would add unneeded parts when unpacking is enabled for the main package, because a buildbase must have the largest set of file, so it must be defined as the main package and have the unpack attribute on.
The subpackages must be small subsets of it, but to avoid the unpacking process. The difference for three python packages, for example, is from 2.5GB of packed buildbase (internally having about 8GB) to 7MB per each of the two subpackages.
But this is not possible to produce due to unpacking that is applied to all the subpackages which will be of 7.6-7.8 GB eventually, as effect.

Describe the solution you'd like

Unpacking should be applied per package and subpackages individually. So hidden attribute.

Describe alternatives you've considered

Additional context