Sorry if it's a dumb question, I'm just thinking about the eventual roll-out of a new parser. I had sort of hoped/presumed that the new parser code would be tried out on a very low profile project first, then slowly rolled out to the other ones.
Both parsers could be in the code at the same time with a config option to choose between them, that way it could be turned on for only a few small projects (I strongly suggest more than one so multiple languages are involved) at first.