Flying next week from DCA-DTW-GRR. Got multiple offers to UG to F for about $39 per segment. Last night the F upgrades finally came through on both of my outbound legs. I'll probably get the GRR-DTW, but the DTW-DCA flight looks full.
I was able to easily use a GUC DCA-ATL-LAX, with the ATL-LAX on the A350. It will. Flight's the first week of June.