There’s been a long-standing thread on the Adobe forums about the canvas size limits in Adobe Illustrator (as well as other Adobe apps) that force large-format users to build files at smaller dimensions than the final output. The forum thread has gotten hundreds of posts from people complaining about this restriction.
In an unusual move for Adobe, they just announced on that forum that they’ve heard the complaints, are developing ways to remedy problem and are soliciting suggestions and inviting people to join their pre-release program for the fix. If this canvas size restriction problem affects you, you might want to take a look. They’re apparently listening on this one — at least for now.