Modersnism,

If the onliest difference are styles, then there is no need for two different arranger models. One would be enough, the only difference would be in the user-configurable style section, where each user would be able to delete all factory styles he doesn't need, and replace them with the styles he use.

Even currently available arrangers allow You to add user styles, the only problem might be that it's not easy to find the style you need. But of course You always have opportunity to create Your own styles.

When You mentioned Motif XS, maybe that might be the way of arranger evolution. Motif XS is not arranger, but it has almost all features any TOTL arranger have (except already mentioned intro's and ending's but that might change easy) as well as some other features not available on any arranger.

But, when you think twice, modern music is already performed, but not with arrangers. D.J.'s who perform (or as they say 'play' in sense of keyboard player) modern music like dance, techno, trance etc. don't need keyboard, they already have 'instrument', their DJ-gear.