I like the idea of updates in whitedwarf this way armies will get there update faster instead of waiting 2 years for a tome or campaing book. (I rather have them free online in FAQ, but that isn't gonna happen).
If Sons are the only ones getting new core battalions it is fine, they have a very limited and unique unit roster. Which doesn't really fit with the generic core battalions. But I think it would be a bad idea to release any other faction specific core battalions.