Why did you change the bootloader chip?
Mainly because the Mini54 is terrible. Back in early to mid 2012, when Teensy 3.0 was developed, the Mini54 and a NXP part were the only viable options. The NXP part was prohibitively expensive.
The KL02 chip is superior in every way, except it didn't exist until mid 2013. Even after it was "released", Freescale didn't ship production volumes for many months. I've been planning to switch to it for nearly 2 years. The change was delayed several times (and more Mini54s purchased) while other things, like the audio library & board, took priority.
Also, one less bootloader chip for Paul to maintain?
So much this!
The reality is I've strongly resisted adding features to the bootloader because the Mini54 is such a nightmare. Especially switching between clock speeds and power modes involves working around terrible bugs in the Mini54 silicon. Nuvoton's broken-English documentation leaves a lot to be desired, as does their reluctance to give honest answers to any questions about the shortcoming of their products. Some things about the Mini54 I even had to discover by reverse engineering.
Freescale's terse reference manuals won't win any writing awards, but they are complete and accurate and written in proper English. Freescale documents their errata. Freescale is also simply much, much better at designing processors and microcontrollers. Those little design decisions don't show up on a high-level comparison of tech specs and features, and most of things you'd take for granted and never appreciate... until you suffer using a not-as-well-designed part.
Presumably, one bootloader chip to rule them all... as the MKL02 can be programmed to support all Teensy MCUs (3.2, LC, and the upcoming 3++).
Yes, the new chip will allow supporting all board from a single chip with a single unified firmware.
The KL02 also will (hopefully) allow me to work on some really awesome new bootloader features in 2016 and beyond. Some of these are things I wanted to do all the way back before the initial release of Teensy 3.0 in September 2012.
The MKL02 is smaller than the 4x4mm version of the MiniTAN54, allows the retrofit of the external voltage regulator on the Teensy 3.x series boards.
Yes, the reduction from 16 to 9 square mm helped a lot. So did the change from 0.4 to 0.5 mm pitch. That and other improvements in the manufacturing process offset the cost of the new voltage regulator.