The perfect arranger already exists!
1)It has unlimited memory for repertoire
2)It does not need electricity to operate
3)It can learn and remember any music style
4)It has a database that recognizes thousands of customers and their favotite songs
5)The cost is free
6)The upkeep is inexpensive (coffee & candy)
7)It supports the principle of "joy" through expression
8)It comes in all colors and sizes
9)It is never too heavy to transport, and still have both hands available
10)It is constantly upgrade-able through study and practice.......

You got it - it's a M*U*S*I*C*I*A*N !
(couldn't resist - the keyboard isn't the arranger, it's just the tool.)Peace.