They are considering if they can skip some features just to retain some lock in, or competition is already too strong for them to do it. That's "under consideration". "Not considered" means they decided that competition is too weak yet and they can just skip that in order not to increase interoperability (for example WebRTC). Implemented features means they think competition has won and they have no choice but to go along even if they didn't want before (for example WebGL).