User blog comment:MetallicArcher/RWBY Volume 3 Commentary/@comment-25405817-20160416010603/@comment-24198837-20160416034557

To be fair, the maiden thing couldn't have been that radical of a change - considering Pyrrha was planned to die from the start and they said they're following Monty's notes as close as possible, I can't imagine the story was hugely affected.

I'm one for the idea that the concept of magical guardians or whatnot existed as a possibility and they decided to flesh it out as canon around that time.