I don't think it's such a good idea. First of all, as Max Factor mentioned, we only explored 0.2% of the Milky Way, so adding another galaxy is pointless. Secondly, imagine the frame shift drive needed to jump over 2.5 million light years in one jump - taking into account that there are no stars in between the Milky Way and Andromeda, the nearest galaxy to the Milky Way.I am all for adding galaxies. Why? Because it allows FD to go ape with bizarre stellar forge settings without ruining anyone's immersion. New galaxy, new rules!
Even if they come up with some "discovery" of a frame shift drive capable of jumping between galaxies, they would probably replace the traditional frame shift drives, allowing you to jump between the Bubble and Colonia in one jump, which would take away the immersion and the sense of how large the galaxy actually is.