Our kitchen was first painted with flat paint and then my wife spruced it up by using a feather duster to put a pattern on the walls. When we decided to repaint, we used a Semi-gloss latex and you can see every feather duster pattern. What do I do next to prepare for a flat latex paint??? It looks like the walls need to be sanded where the feather duster patterns are.
First, what you are seeing is a build up of paint in the patterns of the fauxing. When you apply more and more coats of paint to the walls you will see most of the fauxing disappear. Sanding to remove the pattern will be very difficult. You would have to remove the semi-gloss and the feather duster pattern, a lot of sanding.
Also, when you apply a flat/matte sheen paint the paint itself will blend in most imperfections in the previous applications of paint. Just make sure to two coat all the surfaces.