Germicidal UV could make airborne diseases as rare as those carried by water

I have worked on such systems at Signify: There are numerous barriers to wider adoption except for very high risk situations. For instance: there have yet to be lawsuits to determine the risk of exposing people to UV. As you see in the comments below, any "UV" is considered dangerous by people not aware of the biological effects of various wavelenghts.

Besides this, excimer lamps have a low expected lifetime, of both the light source as well as the filter due to the high energy in the UV photons. This makes replacement (and maintenance cost) a real risk. This could be remedied by similar wavelength LEDs from companies like CrystalIS but these are expensive and very low power (only work germicidal on a short distance).

Prof. Brenner at Columbia University has first foreseen applications of 222nm in operating rooms, to prevent infection during surgery.

On the whole, it would need significant investment in both research, certification and risk analysis for this to become commercially viable, so while some of the technology is there, the market demand so far just is not -- post-pandemic.

there are much simpler and more reliable ways to significantly reduce indoor air contaminents. one is a building method that produces a "floating" slab floor, that has a small gap around most of the walls, and the underfloor space is vented upwards with a chimney, this creates a small but continious air current that removes most dust and other things in the air.

And then the simple expedient of useing radiant heat sources, that while not as lethal as UV, are in fact quite deadly to bacteria and anything tiny with a high water content, but completly harmless to humans and ,animals,plants. Couple this with hard, smooth ,surfaces that are designed so that there no crevices or areas filth can acumulate, useing hard woods,glass,tile,metal,leather/vinyl l,high gloss paint,for surfaces. No cloth, no carpet.While not exactly cosy or friendly, it makes getting home that much nicer. Cheap, reliable, low maintenence, implimentable at scale, now.

Your first paragraph is advocating for ventilation, which is great but there's been so much incentive to reduce building energy consumption (heating/cooling) that recirculating, filtration and other technologies have resulted in offices becoming almost sealed off. We are now moving towards more balanced models as people don't feel comfortable in such offices e.g. sick building syndrome.