The Korg Prologue synthesizer features has a relatively traditional three-voice architecture, until you look at the third voice, which can be programmed by third parties and end users, opening the door for the synth to evolve over time.
Pricing and Availability
The Korg Prologue 8 & 16 voice models are priced at $1,499.99 and $1,999.99, respectively. See the Korg site for more info. Details on the SDK are available at the Korg site.