I understand that .ai files aren't explicitly listed on the list (which was the extent of Canvas Support's help on the matter), but the fact is that for several years the DocViewer did in fact display ai files. What's changed now is that now the screen is completely blank (below left), not even loading the toolbar at the top and link to the submitted file that I see in instances where students submit file types that are definitely not supported, like .prproj files for example (below right). This difference is what's giving me a clue that something it off.
SpeedGrader DocViewer when seeing an .ai file
SpeedGrader DocViewer when viewing another unsupported filetype