Gwynne Shotwell at SmallSat 2016 in Utah mentioned that SpaceX would be using the JCSAT-14 recovered first stage as a fleet leader in wear and tear. That they would be mounting it on the McGregor, TX test stand in between operational stage testing campaigns and running as many full duration burn tests as they can before some unspecified end condition occurs.
That is, run the thing to destruction minus one. (A full up RUD on the test stand could potentially damage the stand, which would affect all operational stages, so would be bad, thus the minus one. Stop just before it destroys the stand or even the stage).
By the end of July 2016 reports suggested that three full duration burns (2+ minutes) had already been run on the test stand, and it had to be removed to allow testing of the AMOS-6 first stage.
This raises an interesting (to me, anyway) question.
How long does it take, if the stand is empty and ready to go, to mount a first stage, run the test, clean up the stand.
Then potentially run a second test, or remove the stage and ready the stand for another stage to be tested.
In some ways this would implicitly answer another question of the maximum bandwidth of McGregor to test first stages. (Number of work days in a year/number of days to do a test).
This also would provide insight into how much of a dent in operational missions the testing of JCSAT-14 will incur, giving a hint of at some of the costs of reusability development.