Honestly on all of my storage machines the sound of the drives is the least of my problems. It's the damn fans! That being said, I used to hang all of my drives from bicycle tire tubes and that eliminated any vibrations. It didn't help with noise as much as I had hoped though.
I'm not concerned with noise from the drives. My issue is with the vibration from one drive seeking while another drive is writing and therefore impacting the performance of the drive writing. Your setup obviously eliminates drive to drive vibration, but would be a challenge to fit in a case with any kind of decent drive density. Also given that drives are most susceptible to rotational vibration, I would wonder if having the drives suspended like that you could end up with self induced reactionary vibration within an individual drive impacting write performance.
So may be a dumb answer, but I haven't seen too much of this being an issue in most of the server chassis and backplanes I have used. You have to remember storage companies like Compellent (even now under the Dell brand) are using a Supermicro chassis. If vibration was that much of an issue, at that level of customer you are building your own chassis. Then again, I get really close to my back-of-the-napkin estimates in terms of performance so I have not bothered to look at this.
I think it really depends on the chassis as to what will work best... I've found that some heavy butyl/foil sound deadening material helps kill vibrations in some of the cases we've put together but it hasn't been necessary on almost any of the newer mid/high-end desktop or server cases we've seen... Once or twice when repurposing old/noisy drives.
Cheap ass tower case from Newegg. I've now got the drives mounted suspended so that they don't transmit vibration. The downside is drive density sucks. Not a problem for me now, but will be as I need to add drives. Investigating benchmarking tests at the moment.
So you're concerned with random reads/writes being effected by vibration? I can't imagine that vibration would have any noticeable impact on reading a large contiguous file. When you talk about drive density it makes me think you are going for storage in which case such performance isn't an issue at all. Just get a SSD for those tasks.