Hi,
Sorry for the delay, been on holiday 
You may not need to expose it, you can access all the native (framework native) parts of a text field via:
myTextArea.getTextInput().textField
Note that if you use that then you are linked to openfl, ie, .textField may no exist on other backends, but if it does, it certainly wont be the same type - still it may be good for testing and something we can expose in a more backend-neutral way.
Let me know how you get on
Cheers,
Ian