If you want 6 to be successful, ask the people that are still playing your most successful entries in the franchise why they still play them. Honestly remake BF4 with a commander mode and US military ranking and medals system like BF2 and you'll win them back.
Just re-skin BF4 with the new engine add portal with hardcore options for the realism junkies and make maps like Jalalabad, Karkand, Golmud, Seine, Bazzar ect.. Battlefield is a squad based team game, stop trying to make it a Fortnight or a COD. Inclusivity is fine but everyone in the military is green so no leopard print m249s, orange Mohawks and wing suits. Keep it military.