Oddly, MIDI-IN is probably not required for the MK-149 as it is the controller, which sends all your playing data to another device which offers voices for instrument sounds (DAW or other keyboard / rhythm machine with sounds). It does not really need to receive any of this data.
Here's some interesting background on the MK-149 :
Interesting Background
Unfortunately, the More Info website shown at the bottom of that page is no longer connected with this product. Bummer..