Always able to do it? Yes. Even before OpenType alternates, the extended ligature support in TeX 3.x would have also allowed for this sort of thing.
Why has no one tried it before? Because (a) nobody thought of it and (2) OpenType alternates, while they’ve been around for a while, have not always been supported in the sorts of programs that use monospace fonts (code editors and terminals)
Comments
Always able to do it? Yes. Even before OpenType alternates, the extended ligature support in TeX 3.x would have also allowed for this sort of thing.
Why has no one tried it before? Because (a) nobody thought of it and (2) OpenType alternates, while they’ve been around for a while, have not always been supported in the sorts of programs that use monospace fonts (code editors and terminals)