I really appreciated getting accurate flight availability information during irrops, when I could say "um, I think there's a routing through Houston available -- can you check UAxx followed by UAxx?". Prior to the 3/3 merger I had to do this with third-party availability data which were slightly out of date, meaning occasional conversations where an agent would say things like "I know you have some reason to think that flight is V1, but in our system it is V0".

If you'd like to know whether there's R inventory, you can still use "advanced search" to find a Y-class ticket and select the "MileagePlus Upgrade Award" check box that also checks for award availability, then check the output to see whether the cost includes $ and miles (upgrade confirmable instantly) or just $ (flight is R0).

You can also do this programmatically. I think as long as united.com provides a self-serve way to see whether the flight you're about to buy can be upgraded, frequent travelers will be able to write software to check the same thing. Since upgrade certificates tend to occasionally get "stuck" (flight > R0, waitlisted upgrade not processed), there will still be a customer need for these data.

(On flights which are sold full in coach, I can't think of a way to know whether there is R inventory.)