One of the rules to come out from the 'first looks' is a constant change from D3 damage to a straight 2. While many will think this prevents swingy results the number of rules coming out that 'reduce damage by -1' is making D2 a little redundant.
Rules such as Guardian Eternal, Paragon Warsuit and the newer Ork Ramshakle rule all reduce damage by 1. Overcharging plasma then becomes a little useless when targeting these units as does wielding a Power Fist, which at one time was the more guaranteed weapon for taking out tanks and larger monsters.
Damage D3 however is still quite effective. Yes, 2 out of three times you are going to only cause 1 point of damage, but you still have a chance of getting a better hit and causing 2 points of damage. A squad of Terminators swinging those fists will be able to deal more damage on average than a straight D2.
I'm not sure why GW is dropping D3 from a lot of weapons, I feel they will have some play test reason, but as a lot of playtesting now seems to be done by the community and by a lot of YouTubers GW likes. I feel that sometimes these folks have more of a personal agender and will want their chosen army to be the best.
I just hope that D3 doesn't disappear completely, I like having some more random damage as this can apply to the narrative you are trying to create (for me anyway) and I feel that replacing this rule just makes the Matched play players happier than the story boyz.
Let us know what you think.