@dennis interesting thought BUT there are a few issues to overcome:
1) The Twiddler firmware is looking for a key press and hold, or multiple presses and hold in the form of a chord, and then a single release to generate the HID packet(s) to send to the host.
2) Morse code can have up to 6 dots in a "packet". We only have 5 rows available for use as dash or dot. We could us the top thumb keys though but you are running out of fingers...
So if you made the Middle column Dot (there are dots on the keys) and Right and/or Left Columns Dash:
"a" would be MR00 . -
"b" would be RMMM -...
"c" would be MMM0 ...
"d" would be RMM0 -..
etc...
So that would mean that all chars become chords. If you know Morse code, this could probably be a viable mapping for you. But having to learn Morse then apply the mapping to the Twiddler, you would probably best served just learning the Standard, TabSpace, or other popular mappings out there. Those mappings will give you a speed boost as well.