Cirrus clouds always contain ice crystals so ice crystals in clouds are not and have never been unusual. I would think the iridescent appearance would depend on the angle of the sun when they are visible and perhaps other atmospheric factors. Cirrus clouds form between 16,500 ft and 45,000 ft so the altitude they are at probably matters too. I would suspect that cirrus clouds are able to form at lower altitudes more often at more northern latitudes but I'm not certain of that.

As far as there being more images of such effects recently that could be due to a number of factors. The obvious one is that they occur more often now as you mention. But it could also be because more people are taking photographs every day or because a conspiracy theory has brought more attention to them. I live in Florida and can't say that I see them too often but now I'll probably start paying more attention and therefore seeing them more often. The problem is perception can be very subjective without collecting actual data. Can you tell for sure if they are really occurring more often or are you just paying more attention?