Im sure a theme API would be really valuable to many institutions. It would make the process of introducing custom JS and CSS into Canvas much easier. This could be an automated part of the build process along with testing when we set up our development environment for the custom JS and CSS.
A theme API would also allow us to programatically track the code that is in our environment, as we are a big institution this would be very helpful.
It would also be good to have a theme history, to show us who uploaded or changed the theme and when they did it.
Another idea here touches on this but im also talking about an API to GET what is in particular subaccounts aswell.