Certain of the things don’t make sense lorewise, mostly the weapon list, some of those weapons would not be available for us, or wouldn’t be effective/useful
As for enemies, there is still a lot they can do inside the Dreg and the Scab, before even having to introduce new factions, but GSC would work, having Tyranids wouldn’t, and Dark Eldar wouldn’t make sense as a Tide.
Short word: Everything they want to develop will take time, they can’t pull thing out of thin air, and they’re planning on releasing things, both known through datamines and known due to past patterns in Vt2.