I have a sort of solution for something like that but it is still work in progress and fairly hardcoded so I can currently offer only the general strategy.
The general idea is to use database
activities with some scripting so you don't hack the core code or use plugins which may make you depend heavily on others for maintenance.
The submission of the online text is to a database activity where a designated Add Entry and View forms which you can design to fit your requirements can offer certain notifications such as word count and late submission. These notifications can be generated by very simple
javascript and even if you don't know javascript anyone with basic knowledge can help you set the required functions which you can add to the javascript template of the database.
Feedback can be given by adding a comment copying the assignment text into the comment and using a very simple toolbar (html table with a bit of js) which you add to the View form and can use to paste predefined feedback into your comment.
I actually use a more complex procedure which involves two interconnected database activities, one for the submissions with its designated submission form and the other for evaluations with its designated evaluation form. The evaluation database is hidden from students. I start the evaluation by one click from the submission entry which creates a corresponding evaluation entry, takes all the relevant information and text from the submission and copy it to the evaluation entry. Then I do the evaluation in the evaluation entry where I have the designated rubric which allows me to add predefined feedback by single clicks. I save the evaluation and then one click on that evaluation entry will copy the complete evaluation and add it as a comment to the student's submission entry.
I realize that this hand waving may not be helpful at all but I offer it just in case you may somehow be able to do something with it. When I have the time I'll try to wrap up something generic and add it to the exchange site.
Below is how the evaluation form may look like (as I said this is work in progress). You place the cursor in the desired location in the text and click one of the rubric items to insert it in that location. The returned feedback may remain in the coded form and students can decode it with a feedback sheet posted on the course site or the codes may be converted to predefined discursive comments.
