This is what I have been able to piece together, from reviewing the Japanese websites and the previous posts:
1. Despite being named Mark X and having a front-end that looks like a Mark X (which is a RWD vehicle and shares a platform with the Lexus GS), this multi-purpose vehicle (MPV) is a FWD vehicle (with AWD option).
2. The dimensions of this vehicle, with exception of the wheelbase and height, are somewhat smaller (shorter and narrower) than the Camry. It is similar in size to the Mazda 5, although it looks much larger, to my eyes.
3. The engine is mounted laterally (sideways, with the transmission beside the engine), as in the Camry, rather than longitudinally (lengthwise, with the transmission behind the engine), as in the Mark X.
4. These items would seem to suggest to me that this vehicle, despite being named the Mark X, is actually built on the Camry / Avalon / Highlander platform.
5. If it is a Camry station wagon, it could be sold (and assembled) in North America sometime in the next year or so as the Camry-based crossover that has been rumoured. If the other rumours are true, this would then be the replacement for the Solara.
This type of vehicle would be new to North America, but is quite prevalent in Southeast Asia and Europe (various Toyota models available such as Corolla Verso and Toyota Wish).
If anybody has any more information, please confirm (or disprove) my speculation. My knowledge of Japanese is very weak to non-existent.
We are in the market for this type of vehicle (if I can talk my wife into trading in her Civic for another Toyota to join my current Gen6 Camry). The new Highlander just seems a bit too large for easy in-town driving.