The Text Field with Formatting is a great new display type that we'd love to convert a lot of our existing fields to. This display type can only be selected when creating a new field, so existing fields can't enjoy the benefits of text formatting.
We are in the same exact situation. We would like to switch over to the new Text Fields with Formatting but do not want to have to create a new field and lose the existing data on our projects.
Same here, we really need this!! We have a specific field we use for basically EVERY project and is very important. I want to convert it to the text field with formatting and every way I can think of to change it to the new field without losing historical data is incredibly tedious and time consuming. You basically can't get around having to manually copy/pasting info from old field to new before retiring the old field. I've been sitting on this for a month not wanting to do it, hoping that WF will come out with this improvement. Please, WorkFront!