I was initially thinking of it more like the Kreol version of "Cockney" (the working-class English vernacular that originated in the East-end of London). Cockney routinely replaces the (unvoiced) "th" sound with an "f".
For example:
The Cockney accent started off as something specific to a small area of London, but over time it became much more widespread among the public (throughout the whole of London) whenever they were speaking lazily, or casually in informal situations.
I arrived at this Cockney comparison with Kreol because I have never heard the 's' / 'h' substitution used by any Seychelles newsreader. I have also never heard it used by government officials, politicians, senior executives, or any other business professional when interviewed on TV. But as soon as the news does a street-interview with someone from the general public (especially if they are a manual-worker type) then I immediately hear non-stop 's' / 'h' substitutions.
But Cockney still might not be the best comparison. Perhaps the phenomenon might turn out to be more the like Great Vowel Shift (which ended up spreading throughout the entire country and subsequently affected every English dialect). Apparently, language scholars still cannot agree on where the great vowel shift came from, or why it happened. It seems to have just inexplicably come out of nowhere and permanently changed the entire language.
One question that I have is: Are there Kreol accent variations between the islands (or regions) of Seychelles? For example, can you tell by listening whether someone is from Praslin or La Digue? I'm not yet familiar enough with the language to be able to detect whether there are regional accent variations or not.
However, one thing that I have noticed is that some people speak Kreol much more 'tonally' than others (it almost sounds as if they're singing when they speak). I really like this because, to my ears at least, it sounds more indigenous and unique, and less affected by foreign influences.
Even though I can't distinguish any regional Kreol accents, I can detect when people are speaking Kreol with a French or English accent (which I don't like as much as a traditional native Seselwa accent). I am also not keen on when people speak what I call 'Freole' and 'Kranglais' - lol (for example, when people speak in Kreol but then include 'posh' French pronunciation for certain words like 'quelque chose' instead of 'kek soz', or when they insert whole sentences in English that could have just as easily be said in Kreol).
One of the idioms that I often hear in Seychellois English is the term "at the end of the day". But a few weeks ago I heard someone on a video say "a la fin du zoor" which I thought was so cool, and much nicer than saying it in English in the middle of a Kreol sentence.