For what it is worth, this seems to have a similar screen form factor to the expanded to Duo, so maybe they were waiting for this announcement before revealing the simulator to make it clearer that apps supporting one of the devices may support both? Not the first time Apple has made multi-device plays on a new form factor.

The HomeView has a 1:1 display, the Duo has 1:1.4 displays. Not really similar. Although I would expect any devs (had there been a SDK) to start with their iPad apps, which are expected to adapt to different window sizes.