As someone with a similar build (Freenas, 8x3tb raidz2 main array, 3tb scratch/hot spare, 2tb scratch, and 500gb ssd for jails)
I would love a rackmount for drive accessibility, but I can't justify 10x the case cost and additional engineering in making it as quiet and clean as my fractal design R4. Rackmount stuff just isn't designed to be either of those, high static pressure fans and expectation of pre-filtered air. (That said I'd totally be willing to pay ~500$ if such a case existed)
I picked up a 24 bay supermicro case on eBay for $265. This came with 24 hotswap bays and even a SAS2 expander backplane so I only have to connect 1 cable from the motherboard SAS controller to the case, and all 24 disks just work.
As far as making it quiet. Well that consisted of buying a $11 fan wall, installing 3 120mm Noctua PWM fans inside it and writing a simple script to govern the fan speeds based on the HDD temperatures to keep them in check with the minimum fan speeds necessary.
It's sitting in my bedroom next to my bed and I can hardly hear it.
I will concede the dust issue, but I have a normal air filter in my room and don't normally have dust issues with my computers. Maybe I clean them out once a year in the spring if they need it.
I would love a rackmount for drive accessibility, but I can't justify 10x the case cost and additional engineering in making it as quiet and clean as my fractal design R4. Rackmount stuff just isn't designed to be either of those, high static pressure fans and expectation of pre-filtered air. (That said I'd totally be willing to pay ~500$ if such a case existed)