Majors will probably reworked - the historical paths will probably be free, alt-history paths will come with DLC (based off current strategy).
Greece, Bulgaria, Turkey, Sweden, Finland, and Iran will probably be attached to DLCs, with Greece, Bulgaria, Turkey probably packaged with Italy.
Vanilla takes a while to create focus trees compared to mods because HOI4 has relatively few content designers (that is, programmers specifically focused on creating focus trees) and most of those content designers also work in other parts of the process. Each update/DLC often introduces new mechanics, which means time needs to be spent playtesting and incorporating new features into the new trees. Art also slows things down - HOI4 uses painted portraits vs photographs, which helps create some degree of exclusivity regarding purchasing DLC vs using mods.
For better or for worse, the DLC model is what Paradox uses for its games. While free content comes along with new DLC expansions, at least a part of each update will include a paid component for the near future.