Is it acceptable to make a text field look like a write in line?

My designer would like to implement a text field that drops down on hover against a white background, and only have a bottom border to define the field. Also, the designer would like to see a flashing cursor immediately visible in the text field as the box drops down - and this would indicate to the user that the field is editable. So essentially the field will look like a write in line.

My thought is that there isn't enough visual separation, or indication that the field is editable. especially against the white background. Am I wrong in thinking this, and should I recommend a different design approach to this box?