It is my understanding, that for a while you will still have the old version of assignment creatation available which of course works like your used to and you can comment inline for online text. Just have to make sure that you do not upgrade the assignment with the Assignment Upgrade Tool.
You can do the same thing with the new assignment, but with two small differences. When you create the new version online text assignment, you just have to remember to set the Feedback Settings to Yes which will give the feedback editing area that you are used to. And the other small thing is that the grader will have to copy and paste the students writing in there, themselves, and then do their marking like before.
So possibly the tracker item that Mary added just needs to ask to have the writing automatically added to the feedback area like we are used to.
PS: I just realized there is a major inconvenience problem with the new assignment when set for online text. You cannot see the submitted text and a scoring rubric at the same time. When you click to grade a student submission, it is only showing about the first four lines of text with the complete scoring rubric below it. You have to click a View Submission toolbutton which then opens the complete text but makes everything else disappear. Gotta go play with this some more to see if I am missing a setting somewhere and if it does the same thing when set to use a marking guide.