Hey I found this forum because I was asking myself the same thing! I think the double roll is really quite useless in AoS, the only reasons I could think of to keep it would be:
don't change the rules too much: this is quite unreasonable since one of the best things in AoS IMHO is the simplified rules, so just go ahead and make them as simple as you can!
wound probability: with double rolls all success probabilities are lowered and in general you have a more vast spectrum of probabilities you can assign to units. This is true, but let's face it, some probabilities are quite useless: a 4+/4+ has 1/4 success rate which already really sucks IMHO, but a 5+/5+ would have 1/9 which is like plain useless. Even a 4+/5+ with 1/6 success rate is like really low. I think in average you'd have 5-7 models fighting in a unit so it's like 1 wound per turn (without even considering the save rolls) -> USELESS! Even a super skilled 3+/3+ character would have 4/9 (less than 1/2!!??) chance to do damage. Seriously if now the rolls represent the chance of a model to make a successful attack, I think 1/2 probability is like the dude isn't even trained. 1/2 means you have the same probability to succeed than to fail. WTF?
unit durability: ok so maybe they want to keep the losses low so the Bravery rule won't waste too many models in a unit making it very short-lived. But I mean, just raise that Bravery value.
more abilities/effects: sure, but duh, I mean you can already have many nice rules with just one roll. You can skip saves (always or on 6s), you can make mortal wounds (just don't roll anything), you modify the REND/DAMAGE (for example 6s to hit have additional rend/damage) etc.
I think a regular human soldier with:
Bravery: 7
Attack Success: 4+ -> still kinda sucks, but much better than 1/4...
Save Roll: 5+
Would be quite fine. Let's consider two human units facing each other with 6 attacking models each. Since they have 1/2 attack success rate they'd deal 3 hits per turn, with 1/3 saved it totals to 2 wounds per turn. Since they're all trained soldiers, they should be ok with some comrade falling during combat, so in this scenario a 1/6 probability to have 1 model flee should be quite fair. A combat like this would last in average 5 turns which in a 6 turns game seems quite fair too.