The plan was other at the start, it was something more similar to new Empire, new Chaos, new Kislev,... Something more similar to Heresy
That was changed for "recover old molds", "recover old stuff", "zero compatibility".
We are talking about plans of 5 or 6 years ago that were changed dramatically for internal stuff.
Other points is the "legends factions", with the actual info that we have and the rumours, if only half is true that implies that Legends factions are not planned to go to ToW. They are squatted at this momment, who knows if in 8-10 years would come. But for now, to me, every rumour that implies a Legend factions is automatically fake without exception.