Has there been any progress on implementing the DataInput and DataOutput elements in bpmn-js? I found this issue, but it’s from three years ago and I don’t see anything since then. I’ve been trying to implement it in my project, since it’s been requested.
Not on our side, sorry. 
Related topic, then, because I don’t know proper open-source etiquette: if I at some point manage to write the I/O elements myself (I might not have time, this is a big if), would it be appropriate for me to submit it as a merge request to bpmn-js?