Sorry for making it confusing.
Augmentations have always been capped at +4, that's not new to 6we.
What IS new to 6we is bonuses from sources other than skill + attribute are capped at +4.
So if you have Agility 4 (8 ) thanks to level 4 Muscle Toner, that's just giving 8 dice in the attribute portion of the Skill + attribute formula.
Things like the Control Rig giving +Rating dice are what's capped at +4. (Ref pg 39) So, for example, you can't get +5 dice from Reflex Recorders, Improved Ability Adept power, and similar. It also means if you have a rating 3 control rig, you can only get +1 more die bonuses from elsewhere, such as Reflex Recorder.