I think it would be really useful to be able to move Clients (and their services/packages/... between different Companies (either main or add-on) on the same license/install.

Example with 1 License (Comp_A) + 1 Addon Company (Comp_B):

Comp_A -> 50 Users (examplecompany.dev)
Comp_B -> 10 Users (smalltestcompany.dev)

Migrate all 10 Users from Comp_B to Comp_A (including their associated Services/Packages).