What happened to 69ers? For a year or two, I remember there being a pretty big buzz around 29" front wheel, 26" rear wheel mountain bikes.  They seem to have fallen off the face of the earth.  What happened?
At the time that 69ers came along, 29ers were still struggling to gain mainstream acceptance and 69ers simply didn't offer enough benefit, if any, to really interest the masses. I always felt that 69ers, especially hardtails, did more to combine the disadvantages of each platform rather than the advantages and so did many others. There just wasn't a compelling reason to mess with such a niche bike at a time when you could count all the 29er suspension forks and tires combined with just your fingers.
Ultimately as we all know, 29ers did gain mainstream acceptance, and when there was room for a "middle ground" platform 650b's filled the gap. It doesn't mean the configuration wont come back- I think it still offers potential benefit in a full suspension configuration, but the first wave of 69ers was not a success. At the time it was an untested platform based on an untested platform that typically cost more than all the other comparable bikes due to the small production runs.