Training hints via an IME

[gotjoshua]

I am trying to setup a way to learn chording during everyday typing.
I came across IME customizations like varnam and i think it could be cool to compile an IME suggestion dictionary from a combos.def file.

My intermediate solution is to use macos text substitution feature.

So when I type thi i see a hint to remind me of the available chord:

but this can only give one suggestion for each combo, and actually when i type
th i want a list of the various options for th...

Ideally, i want a list that allows me to choose which actual word to type and the hint to remind me of the chord.

I think this could be done with a custom IME, perhaps even with a simple fork of the varnam project, but i have zero experience with that level of os integration, so i am documenting the idea and wish here.

Any thoughts or resonance?