UPDATE:
I called Taylor today here are the results:
-For my 714ce, the change to a new preamp began in September of 2016. I stupidly didn't ask if this was the same for every other guitar but maybe we can assume it's similar.
-The changes to the preamp were mostly an adjustment on the G and D strings, and to create more balance across all strings. According to the employee I spoke with, the overall output of the new preamp should be roughly the same. They made the changes due to various issues with the G and D strings like weird resonances. For example, someone in this thread had an issue that would probably be addressed by the new preamp:
http://www.acousticguitarforum.com/f...d.php?t=430496
-They said the new ES2 preamp should definitely still be louder than any ES1 and recommended I go to an authorized Taylor repair place while the guitar is under warranty.
Also, the string spacing on my 714ce's 1 3/4" nut is 1 1/2" from E to e. On every other Taylor I tried it is 1 17/32" which is Martin's standard as well. I asked if they made a change in 2017 and he said no, and that all Taylor nuts are hand cut so there is some variance expected.