Well there would be no filter medium to harbor mold or to replace. And with ultrasound it puts minerals and bacteria into the air somewhat. My designs really on natural evaporation with easily cleanable parts.

Once niche market familiar with is cigar humidifiers. Mold is a constant concern and all of the solutions on the market today either use ultrasound which works great, but causes the problems you mentioned or silca beads, which are much more cumbersome to work with.