It will be great qol option After the merge.
We currently have mixed faction thing at tunisia. Or romanian and hungarian weapons at stalingrad and moscow.
Allowing some gear of both sides as interchangeable weapons and vehicles can solve majority of balance problem about minor factions (italy, romania, finnland)
Brits can equip garand and m1 at tunisia so this must be kept like that.
Italians can use g41 at tunisia.
Or allowing italians to use some german tank units
Other european axis minors can readress some of their lack of armor/fire power.
Its also not ridicilous compared to history. Germany supplied, shared its technology with european axis partners.
Me 210 was the most favourite plane of hungarian air force in real war for eg. But german gave them that.
Lend leasse also is a thing so brits can use some of the american gear ( garands for lack of semi autos, maybe some top tier tanks for lack of armour against germans)
Or muricans can use strong british bolties.