To answer your questions in short?
The ultra orthodox Jewish community. Williamsburg, Boro Park, Crown Heights, Flatbush. Like I said: reporting from "BROOKLYN"...
Israel, and the middle east in general as well HEAVILY use arranger keyboards for gigs like weddings, "bar mitzvah's", etc.

I know for a fact from talking to people here, there are YOUNG people buying keyboards all the time. From Psr s710, korg pa500 to pa3x and Tyros..

And the reason I say its not dying is because thank G-d the Jewish community is thriving bli ayin hara and constantly growing, AND one man band is a staple of Jewish life here. The average wedding hires a one man band, and, thank G-d, there are lots of them. This is partially I believe to limit the overall cost of the wedding which would be raised considerably were they to hire a full band.

Now DIKI, this is the reason we all use custom styles. Because we play unique jewish "hassidic" music, which, unfortunately the keyboard companies do not include styles for...

I'm saying all this to encourage you all, from first hand knowledge, that the arranger, and one man band business is not a dying but to the contrary, "thriving" here and in Israel and the middle east. Thank G-d.