I had the same question and called GBCI two weeks ago. The customer rep confirmed that the MBCAG guideline for v3 is under development and has no date when it will be released. Meanwhile, projects registered under v3 cannot use the old MBCAG guideline. I think it is unfortunate, but I think if you have 2009 projects that you know can benefit from the old MBCAG you can potentially submit a CIR to build your argument.

Under current guidance, every building in your multiple buildings project must be registered separately in LEED Online v3 and grouped by a block. The block grouping ensures that all buildings in the submittal will be reviewed by the same review team. Our project information forms (PIFs) do not currently support data from multiple buildings and as a result each building must be registered separately.