After some research here I am still undecided on are expansion packs possible.
A by me released soldier pack gets additional extensions such as helmets and banner or munitions bags, but can’t used alone or only with restrictions.
And what is with extensions of other packs from different marketplace creators?
I extend the example:
Main Pack 32 x Scifi Soldiers male with main armor parts ca 500 parts for 80€
+expansion: hardhelmets for 30€
+expansion bags and cloth parts +35€
+expansion: female soldier 32x for 80€
+expansion: 64 male and 64 female heads 70€
and so on.
Even that might not be enough as Epic would have to track a legal relationship between original pack creator and one that made add-on. Like what happens if original pack is removed or licensing for add-on is over. Agreements can change with time and it have to be reflected. It can easily become a complicated mess of who is responsible for what.