Somewhat hesitantly I enter the arena of this topic. I basically agree what Bachus says but there seems to be an element in this discussion being overlooked. An argument I have put forward on several occasions by the way.
I have now played arranger keyboards at home for over 20 years and recorded five or six CDs for friends and acquaintances. Many of you are familiar with some of my home-fried efforts.
As I rarely perform outdoors I have the luxury of concentrating on the arrangements of a song and willing the keyboard to fill in my thoughts on it. As an outdoor live performer you are much more limited cause the crowds ( whatever there number) want to be ENTERTAINED. And entertainment more often that not comes by way of recognizing the song and all the memories that go with it. Hence most keyboard entertainers will probably REPRODUCE the song as close to the original as possible. As such the step to midi files, karaoke files, backing tapes etc. is a very tiny one.
As I did a private gig last year with backing tapes I thought it would be nice to record a CD as such, a "quickie " so to speak.The response of all of those who heard/got it, though favourable was hardly any different than the one that I had gotten on the much laboured CDs in which I had gone to great lenghts to make my own arrangements and often entirely re-arrange a wellknown popsong.
In conclusion therfore I think that performing live these days it will make little or NO difference what entertainers use , as long as one is being entertained professionally. In this respect the arranger keyboard has no future. For those who not only like to fiddle with sounds (synthesizers etc.) but want to make entirely new arrangements of existing songs the challenges remain and the arranger keyboard remains a terrific tool.

regards
John

example of using an ARRANGER keyboard to its full potential:
https://www.youtube.com/watch?v=TZvgawOFiB8

example of " why bother with arranger keyboards ", just use backing tapes:
https://www.youtube.com/watch?v=aoFuDN3bHPw&list=UUbaSW7yCrf0Rfpks9L0WvwQ