Originally Posted by
WineCountryUA
If you’re a customer or MileagePlus member without Premier® status, you may be able to confirm a seat on another flight within 24 hours of your originally scheduled departure time. A fare difference may apply even if the same original fare class is available. And don’t forget — you can always stand by for free.
This is a recent change
And this is what I was curious about. But I suppose it's tough getting answers from UA forum experts about what happens when you don't have status when you all obviously do.

I'll report back on Thursday what I'm offered, if anything.