Denali CTP1 added an Event to collect te actual execution plan using Extended Events, but this would be very useful as an action. A good use case for this would be:
I have a parameter sensitive procedure that when statistics get sampled or skewed, plan generation under a sub-optimal value will cause a bad plan that throws off execution time drastically. I could create an Event Session like:
CREATE EVENT SESSION GetSPSkewedPlan
ADD EVENT sqlserver.sp_statement_completed(
WHERE (object_id = 10334249058 AND package0.greater_than_max_int64(duration,10000))
Where I set the baseline duration and can collect the execution_plan when it skews so I have the skewing value as well. I definitely see how this as an Action could sink a system because people don't pay attention to what they are doing, but it would have an amazing benefit under specific implementations as well.
The problem with the query_post_execution_showplan Event is it doesn't return the duration. If it could return duration, it would be possible to make this work as well.