If you use embedded forms they just have to write HTML. the embedded forms are Angular HTML forms…
The example i gave requires modification of the FormTypes.java files i linked to above. It needs to be modified as replacing the formTypes when the process engine is first initialized (using a process engine plugin).
If you are building a app, take a look at: Form Builder (Drag and Drop) + Form Server Validations and the work done in: Integration camunda with Form.io Form Builder
You can use tools like Formio to build the forms and render them in the task list, or as a External Form.