Does any current arranger already do this?
YES!! Yamaha and Korg both have a few pages in their style creation sections devoted to Note Transposition Rules and behavior. See pages 46-48 of the Tyros 3 reference manual. Similar functionality is described on page 119 of the manual for the Korg PA2X. This was enhanced from the PA1X generation, and is roughly equal to Yamaha IMO.

One of the things that makes the T3 special (and its styles incompatible with the T2 and lesser models) is the edition of the "Guitar" type of NTT. For these tracks, it is supposed to emulate the chord voicing as it would be played on a guitar, rather than a keyboard.

Beginning with G70 V3 and the E-50/60/80, Roland arrangers are supposed to have "Adaptive Chord Voicing" (ACV). This is the "Alteration" parameter described on p222 of the E-80 manual. As with the others, Roland allows you to establish the wrap range for each instrument and track, but really as you said, this is not as sophisticated and results in the odd non-standard voicing once in a while.

Also please look at the RETRIGGER (RTR) parameters on p48 of the T3 Ref Manual, and p137 of the Korg PA2X manual. Roland's arrangers (going as far back as the G-800) seem to lack any user-selectable parameters to determine whether a sound should be retriggered, if a chord is released and applied again within the same measure. I posted about this on the Roland forum a while back, under a thread titled "Improvements to Style Composer." Others there misunderstood or ignored my question. Compare this to page 33 of the manual for the Ketron SD5, which offers the greatest flexibility for retrigger, IMO. Please use your insight/ influence to get a retrigger parameter added to the next generation of Roland arrangers, if there is one, LOL!

I have a Roland E-50 and like the features for live play, but when it comes to style creation, Korg and Yamaha are way ahead in this area.
My $.02,
Ted

[This message has been edited by TedS (edited 08-22-2009).]