Alas no concrete date set yet, but I'm looped into the process and it is moving forward. Couple things to keep in mind with this:

1 - I wanted to get the word out really early on this since it was cool news. The downside is that means a longer wait, primarily because...

2 - These are just a handful of titles in Nintendo's busy VC schedule. There are new titles releasing each week so that means a bit of a bottleneck. We basically announced these games as soon as it was possible to do so, which means anything already in the pipeline is ahead of all six MM GB titles.

To clarify: http://www.capcom-unity.com/brelston/blog/2013/07/18/mega-man-game-boy-games-coming-to-3ds-virtual-console

MMII~V, Xtreme and Xtreme 2 are all coming. MMX2 (SNES) is a likely candidate given that it was on Wii's VC, but no update just yet.

Source: Rockman Corner