Yes, they're working on it as 2nd phase- either to San Bernardino which may be the most expensive option or the cheapest way- Lancaster which is connected by Metrolink. Or maybe Palmdale. Perhaps they're waiting for CA High Speed final plans before making decisions.
The Phase 2 option shown on the DesertXpress website, and based on multiple news and on-line reports what they are looking at, is Victorville to Palmdale. Around 50 miles through flat desert. Going through the mountains to San Bernardino with an HSR line is going to be too expensive to even consider until (or if) there is a CA HSR Inland Empire line to connect to at Riverside or near Ontario Airport.
The situation with the CA HSR project and the final selection of the final route between Bakersfield and LA and just how long it will take to build the Bakersfield to LA route adds a lot of uncertainty to the DX project long term viability. There is Metrolink service to Palmdale on the Antelope Valley line. Looking at the Metrolink schedule, an express train takes about 90 minutes from LA Union Station to Palmdale.
One option would be to extend the line to Palmdale to next to the Metrolink station (no idea of the ROW issues with this) as the interim solution while waiting on the CA HSR system to build the LA to Bakersfield corridor. Provide some modest funding to add capacity and make improvements to the Antelope Valley line, if that is possible, and pay Metrolink to lease equipment & run additional special connecting trains from LA Union Station to Palmdale. That would provide a LA to Vegas train service route, albeit with a slower 90 minute leg and changing trains in Palmdale.
Looking at the map, it is around 45-50 miles from Palmdale to Victorville. The DX project is an estimated $6 billion for the approx 190-200 mile route from Victorville to Vegas, some of that through challenging terrain. Call it $32/million a mile. So an extension to Palmdale might run another $1.5 billion, give or take. Not cheap, but the DX system will have to connect to CA HSR or current CA passenger system to be viable in the long run.
There is a complicated mutual support relationship between DesertXpress and CA HSR. The privately backed DX project helps give the CA HSR project more publicly perceived viability. But the DX project needs the CA HSR project to move forward and pick a route between Bakersfield and LA that they can affordably connect to.