2023 doesn't seem possible. This does tell me that they're trying to get it all opened at once though, which makes sense. And as fast as possible, which also makes sense.Some interesting information in that article. Wes Edens says they are "100% committed" to opening the whole Las Vegas - Victorville - Rancho Cucamonga - LA Union Station line at the same time, seemingly in 2023. That is a more aggressive timeline then I have heard for the parts past Victorville.
The Cucamonga-LA Union section is essentially impossible to do quickly, politically speaking, since it doesn't have environmental clearance yet, it requires extensive land acquisition, and, most importantly, it's lots of tiny little parcels through highly-populated land. I see no route which avoids difficult land acquisition arguments. There's no way that opens with the rest of the line, although it's a nice aspirational goal.
Cajon might not be that hard; there seems to be a lot of space next to the railways, US highway, and expressway, and not a lot of NIMBYs on the corridor. It looks like they're hedging their bets there by trying to build to Palmdale and to Rancho Cucamonga simultaneously, which makes sense, since for ridership purposes they really need to get to one or the other. This reduces the odds of delay by having two routes; whichever opens first, they can start running trains.