Every filesystem contains edge case bugs that lose data. The answer to whether everyone reading this story should go upgrade their kernel right now to avoid this one depends on factors like how probable it is that users will hit this one, and how risky the fix is.
The project maintainers are in the best position to make that call.
Delayed extents is probably a normal thing that happens in daily I/O operations. The possibility of it not actually hitting the platters permanently is a scary scenario.
"A single extent in ext4 can map up to 128 MiB of contiguous space with a 4 KiB block size."
The whole bug sounds similar to a problem we had on XFS back in the 2.6.16 time frame. Certain operations were delayed for hours meaning that it was possible for renames/writes not to hit the platter if the machine experienced power loss instead of a clean shutdown, even if sync's were performed.
I think JFS still has that problem, if Wikipedia is accurate.