I did something along these lines with the fingerer. You have three “mod keys” that together define the tuning of the upper eight keys on pico, giving you 64 effective playing keys (thus more than five octaves with chromatic tuning or eight octaves with diatonic tuning). This is imho better than “octave up/down” toggles, because it allows you (with some practise) to instantly jump to any octave of your choice. Still my most favourite Pico setup
You also need my User Fingerings.txt to get this to work:
There are three fingerers with different configurations in that setup.
The imho most interesting one uses the “alternative 2” fingerings together with the clarinette oscillator. This one is chosen by default.
I can remember that this alternative fingerer setup had some problems with some audio units, (could lead to hanging notes), it works without problems with the clarinette oscillator though.
If you prefer diatonic over chromatic tuning then consider to change to user fingering “alternative” (instead of “alternative 2”). That one keeps each note in the diatonic scale at a distinct playing key, so the mod keys just configure octaves 1-8. “alternative 2” on the other side gives you a 4x16 “strings” playing field with each string being a major third apart from the neighbour. So you can play it like a Tau/Alpha in chromatic mode.
Regarding your initial question with the talkers: I am not aware of a way how you can trigger a belcanto phrase “on release”. But perhaps @keymanpal knows a trick, of the still active people he has probably made the most sophisticated EigenD setups.
What you could easily make is e.g. a setup with eight playing keys and eight keys that toggle the playing keys to a defined range per toggle key “on press” (so no “on release” is needed). This would give you the same playing range as my fingerer based setup and retains the capability to press several keys in the play-key area together (the fingerer variant is mono - plus the three poly keys with defined intervals).
There is one caveat though: The talkers and the interpreter are running in the non-realtime thread of EigenD, so if you are playing fast with fast jumps between octaves it could happen that the playing key isn’t “retuned” yet when you press it.
In contrast the fingerer based variant is running everything in the realtime thread, so you can jump between octaves as fast as you can play