I very much doubt anyone has been "furiously ripping out legacy code". The start menu code would have been planned to have been removed from the very begining I'm sure. It was only present in builds upto not to ease the transition of various aspects of the OS with dependancies on it. It is most likely there primarily so there was a robust backup to use when developers were working though issues with the new metro start screen. But now that we're into the RC it's time to cut out anything that doesn't have any use. Microsoft were never going to keep lecacy start menu code and maintain it just for the purpose of power users who want to hack it back into life.
It's most likely the same situation where when VS2010 was developed it worked in GDI mode and WPF mode up until near the very end until the finally removed all the GDI code that didn't have any purpose.
The idea that Microsoft have been "furiously ripping out legacy code" that was never going to be usable my anybody besides being hacked back into the OS is laughable. I gather though there's nothing stopping anyone from writing an alternative classic style start menu from scratch however.