This isn't really the case. I have a completely open bottom intake, no filter at all, and after not touching my case for almost a year I had some dust inside, but not enough to be causing any problems. And I'm a horrible housekeeper, so it's not like the thing is in a dust-free environment. I daresay any case regardless of intake position or filters would have some dust in it after a year. A much bigger issue imo is that in a cluttered environment things could get piled around the base of the computer, starving it for fresh air. In a one-off case like mine, that's not a big deal, because I can just be smart enough not to clutter there, but a manufacturer has to think about things like that.

Perhaps, you gotta think about a lot of things....what if it is on really think carpet? I don't now how it will perform but its a novel idea for SFF (assuming you use the bigger cases like Qmicra and Micro Fly). I have both the Micro Fly and Qmicra out right now and I am looking at them to see if front 80mm placement would require foot replacement....it seems like the Micro Fly does and Qmicra doesn't.

Any ideas on how I should do a test?

Welcome to SPCR! (That's what we do here.)

obviously :p but would it be worth it is the question! You could make a case 100% silent by getting rid of all the fans...just don't look for it to be up long