The new rules do not prohibit putting the pads halfway up your elbows ? So I'm not sure why you'd reach the conclusion that the aerodynamic advantage will be minimal for riders such as Ganna because if a higher hands position than they have now (like Remco's position) is advantageous, they'll just continue doing it but have their extensions go 40mm higher.
Also, the rules are inherently dumb. It's not a maybe. Having rules that make the amount of stack you can have as a single number regardless of height is obviously extremely unfair for larger riders, because to produce the same position of a rider with shorter arms, they require much more.
The rules originally were there to stop riders from having a super high hands position, but like most things with the UCI they were implemented in a completely moronic way. Like they were fanboys of short riders. Realistically, they were too stupid to consider that a single limit for all riders is obviously unfair. If you look for prominent TT'ers currently, I'm sure you'll know who has the highest hand positions and it isn't the tall guys using single finger grips, or pads up their forearms.
Kung, Ganna, Wout, Asgreen, Dennis, Thomas etc. will all be able to make somewhat significant changes to their positions next year.