I've decided to remove support for multiple authors per story (introduced in 2001).
This functionality has very low usage (96 stories out of over 53,000 or a little under 2 per 1000 stories).
However, this functionality has enormous code impact. Every SQL query on the site that displays anything to readers need to account for this. Every sort by author search needs to account for this functionality. 334 SQL statements in the site's code reference this support.
Joining tables complicates SQL code. Joining tables has performance impact.
All, to support something that's hardly used. I've looked at the stories involved, many of them it was editing support. Most of them have completely absent collaborators. Many collaborators created accounts and pen names and never even logged in after the initial creation of the pen name.
So, it's time to do away with this feature and simplify the site's code.
As for Interactive stories, well after six years we have 9 stories and most of them were never updated and several have no real branches, so it's also a failed feature and needs removal.