For professionals yes, however, arrangers are for the home market, and if that was included as standard then they would alienate 99.9% of the arranger user base.
If it was an addition that could be added to an arranger (Much like Yamaha do with their iPad Apps) then it would be good, but again, only professionals would be interested, and would know how to set it up using 3rd party software anyway.
Remember, arrangers are designed to be simple to use, (Yamaha forgot this with the T5 and sales have been dismal compared to previous generations) and with the market declining, (At least in TOTL) manufactures do not want to put even more people off.
While it would be nice to have home and professional in one box, in most cases I would say it would put more users off, then turn them on. (Nice to dream though)
Bill
A) There is so many professionals using arrangers that your statement that arrangers are for the home market, is totally untrue. While Yamaha still often keeps the home user in mind, Roland Casio and espescially Korg keep adding features based on the demands of pro players, not based on what home players wish for.
B) the fact that you state that only professionals would be interested indicates that you underestimate a huge group of the home players.. that are looking for tools to improve their performances..
C) With a feature like this, they would be able to become the ultimate EDM keyboard. Pulling in much of the youth..
You can add about anything to an arranger keyboard, if you only make it easilly accesible ...
However, if i am right, Yamaha is going to fully aim at the pro players with the Genos.. and going with a PSR pro series for the home players.. However, mark my words, most aspiring home players will follow the pro line..