Thanks for your response, Melita. That's interesting that ESRI will support time/velocity based transformations in the future.
My Trimble rep says a new "universal" coordinate system is coming in the next few years that will automatically account for tectonic movement so that we will no longer have to take this into account. I'm not sure how this would work, but I'm guessing our whole GIS would need to be transformed to support it.
Is it correct to assume in 10.4 that if my collected data (RTK or post processed) is referenced to ITRF08 (epoch 2005.00), that it would not need to be transformed (read = a shift in position) to WGS1984, other than for projection bookkeeping? But if it was referenced to ITRF00 (epoch 1997.00), it would need to be transformed to WGS84 (shifted)?