show build status of current branch

And lots of other error handling so you don't have to open the console.
That's a reasonable solution, do the original poll to see if the project as a whole can return any builds, and if not, shut down completely. I would not do something like exponential backoff because then the interval would be inconsistent and confusing (unless there was UI saying when it was going to try again).

Given that the user has control over the interval, maybe a longer default interval (30-60 seconds). Personally, I think this is premature optimization for a single API request in a text editor (I work on a coffeescript game engine where we are doing hundreds per second in Chrome).