Based on my experiments on Lama, resetting a tree to respec enhancements isn't a big deal...the first time. But if you are trying to figure out the new system, you might reset trees many times in a short period of time, and it can cost hundreds of thousands of platinum.
For spell swaps, there is Blood of Dragons, that lets one freely swap spells for 1 hours.
Could we get a similar mechanic to allow us to freely swap enhancements for 1 hour, before the enhancement pass goes live? Maybe as a rare drop, and 1 free to everyone when the change hits? Otherwise the transition is going to be very painful and expensive.