I'm not fond of the idea of squads having multiple wound models to track. And if it does lead to the meta leaning into mulitiple damage weapons, then they're just creating a treadmill where the "lesser" weapons get left behind.
And what's that they're saying about meltas getting more shots?
Missed that. Multi-meltas go to Heavy 2.
Oddly, because of the way the wound allocation rules work, it's not that hard to track. Each attack is allocated to a model (and you resolve each attack one at a time, no assigning all the attacks to one poor schmuck). If the model already has wounds the attack MUST be allocated to that model.
So if you have ten Marines (2 wounds), and they suddenly come under fire from a Lokhust Heavy Destroyer with an enmitic exterminator (Heavy 3d3, Dmg 1). Let's say the Lokhust fires six times and hits five. The Necron player then starts rolling for wounds (Str 7 vs T 4 for Marines, so 3+). He's lucky and racks up 4 wounds, which have to be saved at 4+ (the weapon is AP-1). Marine player only saves half the wounds, so 2 damage has to be applied. Because of the aforementioned allocation, all the damage (2) gets dealt to one unlucky Marine.
Now, let's change the scenario a bit. The Destroyer in this case is using a heavy gauss cannon, because he's confused and thinks the Marines are actually a tank. He puts a single Heavy shot into them. I don't know if heavy gauss is a blast weapon yet, but we'll assume it's not for now. One poor Marine eats a Str 9 AP-4 shot and takes 5 damage. However, this is standard damage, NOT mortal wounds, so the overflow damage doesn't hit the rest of the squad (that poor Marine's geneseed is a writeoff though).
There is an exception to the 'overflow damage is lost' rule though, and that's mortal wounds. Normal damage is applied first, but then mortal wounds, and mortal wounds WILL overflow and hit other members of the unit.