Hi Steve,
I only have an old psr1500 so maybe the newer T4 may already have these functions.

Sustain controller in style tracks.
Ability to have different time signatures for style parts.
Dedicated fill buttons as well as automatic fills.
Ability to Export & Import a complete style as a midifile for editing in a pc sequencer.
Ability to event list edit any factory style track.
Ability to import a pad as a style track & vice versa.

Something along the lines of Korg's Guitar Mode for creating guitar tracks.

Above are some of the reasons why I have a Korg instead of a Yammie, even though I prefer Yamaha type styles.

In short, better editing functions for styles.