A modern day workstation has the following features..

Full fledge midi sequencer and audio track recording.
16 part layer and split possibilities..
After touch..
separate outs..
Sampling..
Pads or key trigger audio..
Extensive sound editing..
Extensive effects editing and routing..
Ample memory and storage..
Audio and midi interface..
Mixing capable and mastering tools.


Now you can tell me if a Genos, or PA4x, or SD9 are workstations..

Actually the closest arranger keyboard to meet workstation benefits... may be the BK9..

Of the current models I would think Korg is closest to a workstation..