Steinway was an American company (founded by a German immigrant) that later began a subsidiary company in Germany. They are not a European company. No one invented the piano any more than one person invented the violin or the guitar; it was the product of a couple of generations of development by many, many individuals taking innovations copied from others and refining and developing them. And yes, countless Japanese and other Asian-Pacific companies have manufactured and marketed direct copy and imitation products, but Yamaha has never been one of those. I find it amusing that someone might suppose we would need informing of who Yamaha is -- they've been a well-respected manufacturer of musical instruments for much longer than I've been alive.
The concept of having the amplification in the speaker cab would be neither unknown or innovative in 1969. WEM was employing powered PA cabs for several years by then. And of course, the concept would be most familiar to Yamaha because it was almost exclusively the way electronic organs were amplified -- with external "tone cabinets" that had the speakers and the amplifier in the same package. This was common even in organs intended for home use, at least with larger instruments. Leslie is the most familiar, but all electric organ makers offered powered tone cabinets, and I'm almost certain Yamaha was always a player in that business. In fact, with the packaging this way and the rotary horn, I'm more inclined to believe this was intended for the portable electronic organ market. Also, in 1969, manufacturers hadn't yet given up the accordion market either. I'm sure this would be a bitchin' amp for an amplified accordionist. Don't laugh... it used to be a thing.
The use of all slide potentiometers, however, would have been fairly innovative for the era, IMHO. Only custom-built studio consoles had slide faders at that time -- I can't think of a manufactured pro audio product at that time that had slider/faders. The graphic equalizer was still a couple of years in future at that point.
One last point is that Fender offered a rotary speaker cab for a while, co-branded with the Leslie name in much the same way as the Fender/Rhodes piano was. It did get the effect, sorta, but didn't put out much sound. I presume the Wawwaw nomenclature on this Yamaha is referring to that effect. Too bad it doesn't have a speed control... of course, even a real Leslie only has two speeds.
