What are the current Cajon running speed limits? I've never actually been told what the limits are.
As to the fares on that route, I could see lower fares happening if you had a lot of seats opening up at Victorville. However, Metrolink charges over $12 for Palmdale-LAUS, so I would expect that DX (or a truly fast commuter operation) could probably force that up quite a bit with faster times (i.e. fast enough that driving will often not be competitive even if the flow is good).
As to the fares on that route, I could see lower fares happening if you had a lot of seats opening up at Victorville. However, Metrolink charges over $12 for Palmdale-LAUS, so I would expect that DX (or a truly fast commuter operation) could probably force that up quite a bit with faster times (i.e. fast enough that driving will often not be competitive even if the flow is good).