Hello Sack
The concept is not new, however due to advancing computer technology pure software based system keyboards will become the norm. (In 5 years from now the Hardware Arranger that we know today, will not exist, you will just buy a keyboard which has a display and button layout that you like, and then load in the instruments you require).
It was first bought together in the middle 90s when Steinberg introduced the VST Host, which allowed manufactures to have a common interface for there software instruments. (This being purely for computers at the time)
In 2000 Wersi introduced the Abacus keyboard with its OAS system, which in its simplest form, built the PC into the keyboard, and developed a program that connected all the keyboard controls to the computer, they then added a software arranger so that for all intents and purposes, it operated just like a normal Hardware Arranger Keyboard.
As it was a computer, Wersi installed Steinberg�s Cubasis VST sequencer (With its VST Host) which meant for the first time you were not tied to what the manufacture gave you, but could choose what you wanted.
As like all computer systems the Wersi has been updated over the years with new features and sounds added etc. (Current version is OAS 7 which includes its own VST Host)
Over the last 2 years or so, other manufactures have followed, such as Lionstracs, Korg etc, however apart from Lionstracs they have all had one thing in common, in that they were expensive, fortunately as they could easily be updated, (As any computer) mainly by software, in the long term they actually work out cheaper.
Hope the above helps, and look for a rash of products like these, over the next few years.

Bill