I know there was an expanded for the TXo, this allowed for some basic wave folding and such, but I do not know what differed between the traditional TXo and this one. Might be worth asking @bpcmusic or another user what the difference was between the two and if we can achieve it with our current boards or if we’ll need to wait for those.
EDIT: just looked at the TXo+ page and it turns out that it is a small expander to add a teensy 3.6 to the board instead of a teensy 3.2
This same thinking is why a teensy 4 wont work; different physical pin outs different internal structure for communicating with the TXo. Maybe in the near future we’ll be able to buy the expanders, as they’re not very complicated (honestly, if the firmware and PCB’s were made public, I’d just get it printed since it’s really quite small and simple).
So yeah, no teensy 4, and the TXo+ currently isn’t on the table either.