you would probably need to very diverse arranging/orchestrating base. I think there is potential as a staff arranger for publishers, but those guys to my knowledge do all sorts of arranging and transcribing, it would be difficult to find full time regular employment with such a niche specialized genre. You'd probably get a chance to but would also be doing technique/method books for graded repertoire, seasonal tunes, etc. and probably might be asked to do instrumental arranging too. it's the only way i can think that it would make sense to employ an arranger full time in the current market.
I don't know if it's such a niche market - I mean I can listen to anything and arrange it for the piano - granted that the quality of the product depends on the original source. You ask me to try and arrange a rap song, it ain't going to go down well on paper. Yes, I can music for Video games and movie music but if I had to I could arrange Musicals (I know... I know ) or songs if it got me a job.