If the pullout is due (at least in part) to customer dissatisfaction with tiny RJs on a somewhat long route (for such a tiny airplane), then this is very good news. Every journey begins with one step, and customer pushback to all-coach, all-30-31 inch pitch RJs is a great first step.
In part, it illuminates the pressing need for some consolidation in the USA domestic market. As the OP points out, four other airlines (two of which are CO's "partners") fly mainline jets to PSP. As passengers migrate to LCCs on many routes and as airlines offer more and more frequencies (very important to higher fare passengers), they necessarily have to fly smaller and smaller airplanes. And so many former mainline routes have been RJ'd. Especially on CO.
If the big six consolidated into two or three larger legacy survivors, some duplicative hubs could be shut down and frequencies could be maintained on, get this, LARGER airplanes (over fewer hubs). And those larger airplanes could even offer First Class. And with fewer hubs, some routes might even support point to point service.
We really don't need six legacy airlines operating numerous hubs all over the country trying to be all things to all passengers. It leads to things like 3 hour RJ flights going head to head against several competing mainline options.