I'm not sure about that jut northeastward in blue on that map, though. Who up there wants the Gold Line to go there? Or, who DOESN'T want the 8th street route to keep going straight east to the Creek?
Also, they have Metrolink's Right of Way just north of 8th street. Piggyback that ROW, and done.
What Montclair, Upland, Ontario, and Ontario Airport need to do is to create an efficient system of getting to each others transit centers. Or, failing that, try to build one for the whole area and push trains, buses, and light rail to it. I like the former more, since more is already built. But if the latter is chosen, there is a big empty lot just north of where the Ontario Convention Center is, north of The 10 and the airport on Vineyard Street (former site of Ontario Speedway??). All current transit centers can feed this one spot with lots of parking, End of Gold Line, dedicated loop train to and from airport, etc.
Then, they should extend the runways all the way to The 15.