Here is the US WorkStations, synths, digital pianos out sell arrangers probably 10 to 1. If you are going to invest your money in the music industry, guest where it will go.
Go to any of our big music retailers stores (Guitar Center and Sam Ash) and observe where the customers go:
1- Guitars
2- Drums and other percussion instruments
3-Keyboards (no arrangers)
4- Wind instruments
5- Speakers and amplifiers

and then, in the way out they maybe will notice an arranger and just pass by.

Another factor is the education system. Observe the parents looking for instruments for their children in school, they never ask for an arranger.
Most of the arranger use in US is by people 40+ years old.
Arrangers are no used in Churches either. I only know 2 churches (from around 500) around here that use them.
Investment is going to be where the market is.