Put in an option to add a new tab. (Like in the official Processing IDE)
I'm not sure if this has been addressed elsewhere but I would find it useful! I like being able to separate out different aspects of my sketch, otherwise the file can get a bit long and confusing.
It is now finally possible to break a sketch into multiple files. This blog post explains how to make use of the new feature: http://blog.sketchpad.cc/2015/10/multisketches/