Setting aside possible ADA compliance questions with regards to level boarding, CA would not be starting the Coast Daylight as an "experimental" service. CalTrans and UP still have to agree on what minimum track improvements are needed before UP relents and allows the Coast Daylight train to run on their tracks, but CalTrans may have to lay out $30 million to $40 million for track and station upgrades. Possibly more. CalTrans is not going to spend that kind of money with the intent of running a temporary experimental service. The communities on the route won't take that position either.
A Coast Daylight would take 2 consists, but it also would be treated as an extension of a Surfliner slot, so one Surfliner consists becomes a Coast Daylight. Figure a Coast Daylight train would be 5 to 6 cars, and if 2 new consists are needed, worse case 6 cars * 2 consists plus 3 spares means that CalTran might order 15 additional bi-level cars to support the Coast Daylight. At ~$3 million each, not a big deal for CalTrans with the Cap and Trade revenue coming in.