In sample app, I tried to create a text area field as mentioned above. However, I couldn't. I just saw in the configuration a regular text field and not a text area.
this is definitely a good idea - not supported yet.
btw - patches welcome...
PR available: https://github.com/wcm-io/wcm-io-caconfig/pull/29
implemented in Context-Aware Configuration Editor 1.7.0, thanks to