Interesting, I built a similar system for my Vim setup that I slowly adopted over time. I realised that semicolons are almost always followed by whitespace or newlines in normal use, so I started defining a whole range of shortcuts with `;` as a prefix. As the key is directly on the homerow it's also quick and easy to use.

For example I have `;out` defined to expand to the correct stdout print function depending on the programming language used in that file.

Espanso looks like it's a great way to expand the same concept to the whole system, albeit (I'm guessing) without the contextual info a text editor can provide.