Yes, like mentioned above, the main idea could be that they wanted to prevent 'tanking' by use of 'illegal' formations. Well, still managers can use a ST as a GK. Or a GK as an AML. They may still tank, not? And playing around with the game engine is not the best method (although Nordeus do it).

But since they have decided to correct their policy on illegal formations, I wonder why haven't they launched a list with predefined formations, so users can pick what they want.
With rules being now as they recently changed, managers can still having the same formation (eg 4-4-2) but in the eye they may look quite different, depending on where the players are placed in their position area. Eg a DL can be up-left near DL/ML boundary line, or down-right on the borders with DC.
We may see legal formations but quite unusual if you look at them as a picture.
Maybe their next move should be to have certain places again, like it used to be before, for each position.