Main author of Quasar here. The big question is what do "the majority of applications" tell us? A lot of applications run on virtualized hardware, which basically runs a few Pentiums on a single i7 box. So "the majority of applications" don't really need more than a Pentium. But is that really by choice? Or is that simply because modern hardware is so much harder to fully exploit, so we just don't bother and lower expectations? I think it is the latter. If we make it easier to fully take advantage of modern hardware (its processor and memory architecture, its IO/processing latency ratio etc.) then all of a sudden you'll see how most applications actually need every inch of performance they can get their hands on.
The thing I like about it is that you get the async possible benefits without the logical overhead. Erlang allows many connections to queue up on a web server. Now Java can too.
I think if done right, this will bring down costs for scaling. I recently looked at Linode and AWS. My first thought was holy crap! To get a small 2 GB Ram box is rather expensive. It would be cheaper to just pay for a business internet connection and host my own boxes. If I had a spike in connection with normal threading on a small box (my laptop with 16 GB), Java would start to sputter around 200 threads due to context switching. Connections would be rejected. Quasar server would accept the connections, just have a high latency. I could live with that.