Dress casual is definitely on the decline. Just wandering around the central business district in Hong Kong it is obvious that the proportion of (assumed) office workers who are wearing formal attire compared to those dressing more casually has risen steeply.
It's not too hard to understand the cause. People who are worried about their jobs, want to look more professional and serious. Those whose jobs involve dealing with clients on a face to face basis tend to need to dress to a similar standard as those clients - if the clients start wearing suits then those wanting to do business with the clients will also wear suits.
Sadly, I am in that position - the number of my clients wearing suits instead of business casual has risen and even before changing jobs, I was having to change my dress habits to match. At my new employer, wearing a suit is more or less compulsory.
I miss dress casual.