I've been noticing a proliferation of the pronunciation of street as shtreet, strong as shtrong, etc. Have you noticed this too? If so, why this pronunciation? Why the increase? A regionalism? Any other insights you might be able to share about this phenomenon would be great.
I have not noticed that at all. It seems to me like some actor affecting wearing denture.
It is fairly common, and not so new. It is a kind of palatalization in certain phonetic contexts. It is often associated with urban dialects in the USA. We have discussed similar topics before.