Simplified Atomic Composability (let’s call it AC for now) just means more and different information can be in one transaction.
In an article there is the exemple of a flashloan which gets possible through AC but is this not already something which is possible in ETH?
Or is AC just making it more efficient and less pricy
From my understanding, the real problem is:
Now that system traffic is experiencing congestion, eth is contemplating breaking up the Ethereum blockchain so as to spread traffic, but doing this you would likely break atomic composability.
What do you obtain from breaking AC? Breaking AC 
no atomicity lack of flexibility inside the network .
So, replying to your main question: YES, YOU ARE RIGHT. AC is already something which is possible in ETH. Not surprisingly, there has been concern recently about whether or not the “composability” property of Ethereum will be preserved in an eth2 cross shard context.
However, as you can see in this article
Radix has attacked this problem head-on with a new consensus design called Cerberus that is the end result of seven years of R&D. Cerberus introduces two significant changes from other scalable consensus protocols that give it practically unlimited scalability without compromising free atomic composability.
First, Cerberus uses a different kind of sharding. Rather than split dApps or assets between a static set of shards, Cerberus uses a practically infinite set of shards. Assets and dApps are represented dynamically across these shards. The result is limitless parallelism, meaning that no matter how much demand there is on the Radix network, natural financial incentives can just add more nodes to split up the load and increase throughput to keep up. This doesn’t just raise the ceiling on scalability; it means there is no ceiling .
Second, Cerberus removes the barriers between its shards with a completely new consensus design. While each shard is able to conduct fast, secure consensus independently, Cerberus can directly “braid” these consensus processes together into one – atomically, and on-the-fly for each individual transaction. Braided cross-shard consensus is just as atomic and secure as simple single-shard consensus, meaning that composability is just as free and frictionless as on a single blockchain, but without the scalability limits. Cerberus gives Radix shards SpaceX satellite internet, rather than messages in bottles.
My consulted material:
Thx a lot thats puts some good light on it!
This sentence all most made my head explode had to read it out loud and very slowly to understand it
Gonna dig into the source list a bit. Still a lot of black spots which I need to fill
But is this not potentially giving the room to attacks like Solona is witnessing?
Ahah, I know how you feel. We are on the same boat: too many “what if?” and too many doubts for us ordinarily mortals.
Interesting point. Try to give a look at this article full of Vitalik’s suggestion: Why sharding is great: demystifying the technical properties. Maybe the answer to your question is here.
Yeah definitely can feel very ordinary mortal when learning about that stuff
At some point the smart sounding words just mix into a word gibbierish salad but there is just so much to learn especially cause everything interlocks and is important to the full network
Thx for the article I am gonna check it out