no - but i was tempted to do a lower-power arduino, but decided that keeping it on the same platform made the most sense from a DIY perspective. the tooling that has been created for the teensy (especially the bootloader on the MKL04/02) makes ground-up builds and modifications very approachable.
yes, the 3.2 is massive overkill for the TXi. the speed is put to some use making reads as responsive as possible. back when i was designing them, i2c reads over the bus was unexplored territory. i figured making reads to be as fast as possible so that there was little to no impact on the teletype’s timing would be a good thing. ignorant and paranoid? yes.
ASIDE: as a consolation, the TXo uses every drop and then some of the Teensy 3.2/3.6 with its extended features. in addition, because of the teletype’s decoupled and programmatic control, all changes are run at audio rate for maximum smoothness and responsiveness. (audio rate on the unit is 25 kHz / 15.625 kHz for the TXo+ / TXo, respectively.) this means that SLEW is buttery-smooth. 
if i ever do a refresh, i certainly would simplify things a great deal and move everything on-board with processors that are tuned to the demands of the individual modules. might be less fun to DIY at that point as you will need toolchains and programmers…think diy mutable challenging.
