From an engineering perspective I wonder how sustainable that is. For every new DLC X you need to test with (X-1)! combinations of previous DLCs. Sure, not all DLCs interact with each other but many will in some limited way.
They have been following this model for years, CK 1-3, EU 1-4, Victoria 1-2, Stellaris. So it seems to be pretty sustainable?
It is a common joke among fans for these games that Paradox Interactive does not have a QA department, given how incredibly buggy their DLCs are at launch.