Okay, here's something really cool.

We already know that the Beta site will show SQ award inventory (I and X) when you run a search for a revenue (not award) ticket.

I just discovered an added feature: the Beta site will only show I inventory on flights that are bookable using UA miles. And it shows the inventory even if I=0 on that particular flight. So, for example, if you're looking to book HKG-SIN, you can see I inventory on the flights operated by the 330 and 772, but not the ones operated by the 77W.