Snowman --
Thanks for feedback. I imagined this feature could be useful in a couple of contexts, though mainly in the sense of documenting query optimization efforts.
In one case you may be tweaking cost parameters and having a built in record of the parameters in the explain output can make that more reliable.
In a support context, it can help communicate all the details behind the selection of a query plan, perhaps on IRC support.
David J. --
I originally conceived the notion for the feature while off in the deep end thinking about automatic cost parameter selection.
It seems plausible that the ideal theoretical costs would be influenced by server activity (io/cpu utilization) and various buffer states at a point in time. This kind of optimization work is a little beyond my understanding and capability so this was a first step in thinking about this topic. It turned into a trivial user text output feature, but implementing output formats that are more machine friendly still makes a lot of sense.
Best Regards,
-Robert