Would there be any demand for an open-source, more code-oriented version of IFTTT for the devs around here?

So still the same concepts of inputs -> outputs, but you would self-host on AWS Lambda / Azure Functions / etc. It would also have more flexibility to add custom code if needed to transform data too.

https://nodered.org/

Those projects already exist, you are probably better off contributiing to existing ones rather than creating a new one.