"When it is finished" is the accurate answer that's always right no matter what the project. That said I'm gunning for end of month, don't be surprised if it's the end of April. I've been extremely gunshy about estimates lately cause I've missed so many - however I think that this time I'm on target.
Note that 100% replacement of all current features will be further off in the future, but within the year. Rather than try to get everything done all at once the conversion will be in more managable stages - starting with news and forums, then reviews, then galleries, then links. And a bunch of other stuff I'm forgetting I'm sure. This is a huge site - overhauling it is *not* fun but must be done.