This model will have all of the data that the view will display. The templates will json-encode the return value from your ArchiveReviewUI.get_js_model_data() method and pass that into the constructor for your model here (which is how data gets from the Python on the server into JS on the client). In this case you'd probably have some kind of tree data representing the archive contents.
The view then takes the data stored in the model and displays it.

Should be using single quotes

These should all be single quotes as well

single quotes in the print statement for strings

Let's make sure that everything after base here stays in alphabetical order.

This should inherit from object

This should inherit from object

I'm sure it's already on your radar, but this is kind of backwards. We should check explicitly for application/x-tar when instantiating the TarArchiveFormat, and the else clause should raise.
Inn fact, we might want to have a dict mapping mimetype to the format class so it can just be something like:

try:
    archiveFormat = self.formats[self.obj.mimetype]
    archive = archiveFormat(self.obj.filename, file_bytes)
    data['archive_hierarchy'] = archive.to_dict()
except KeyError:
    raise NotImplementedError

We can probably leave this out for now. Unless you're planning on using backbone routing to add a bunch of separate URLs that are all served by the same view, we won't need this.

Have you given some thought to how wide the indent would be for each directory level contained within the zip? You may have to make the default width of the Name column match the string length of the deepest file with the added indents (i.e. if there are 3 levels of directories then the minimum width of the name column should be the width of the longest filename is this directory level with three indents). If you want the Name column width to be fixed for all zips, tarballs or other archive files then you may need to speak with the mentors to figure out the average number of directory levels in zip files to calculate the average number of indents that will be required). 
If you are interested in considering an alternate way of displaying the different directory nesting levels you might want to consider subsituting the indent with the relative path for the file as shown below. 
test.zip

file.text

directory_name

directory_name/other_file.text

It seems like there is a lot of room for the table to grow within the File tab. Some questions you may want to think about: 

-Will the name column have a max width? If yes how will that max width be calculated relative to the window size and file tab size. 

-How will you display file names (with or without indents) that exceed the name column width? Will you use a scroll bar? 

-If you use a scroll bar where will that be place to avoid text being covered (either column name or file names)? Do the scroll bars used in the rest of Review Board work with your design?

I think this is a good idea. I think a seperate download button will make things a bit clearer for users that haven't used this feature before. You'll just need to take into consideration where this download button should be placed and how easily it can be found at different screen widths.

It should match any other tables that exist in review board. An example would be the dashboard that displays all review requests but before you start implementing this it might be worth asking one of the mentors if there is another table that would be a better reference for you to use.

Maybe a drop down/popup that appears when you hover over the file name?

Your work looks really interesting. I have some questions that are just for my own knowledge and also to get some clarifications on a few things. I also found a few white spaces that need to be removed. I'm not sure if you're there yet but you may want to update your mockup just so that when you want to start implementing you have a clear design that you can work from. It might save you time instead of having to design and implement at the same time. Keep up the great work!

What were you thinking you might use for this extraction? Are you considering a third party service or are you going to code it yourself?

For my own understanding, why are mime types guessed here? I've never heard of that before.

Why is "wah" added to the end of this?

There is some white space on lines 7,8 and 12 that needs to be removed.

I think this whitespace needs to be removed

Michael, your project seems so interesting for sure! The minor and general slips that I've seen are for the import statements, where you need to sort it alphabetically, e.g
```from reviewboard.reviews.ui.archive import ArchiveReviewUI
 should come before the 
```from reviewboard.reviews.ui.base import register_ui

or the from xxx import C,A,B

 should be from xxx import A,B,C.