There re a few things popping up that may relate to Terra and Geo-Force in issues around Brightest Day.
A strange portrait of a female member of the Markovian royal family, who looks a lot like Tara Markov, appears in DC Universe Legacies #2 that just came out last month. The only catch is that the story is set in DCU's 1930s and the portrait looks like it dates from the 1700s or earlier. But of course the Tara we know died in the 1980s. I just did a blog post here - see also my Comic Vine blog on this, the post is attached to the CV Off-Topics forum.
In the latest Outsiders issue, GF has just recovered Halo from wherever she disappeared to by using a big mysterious glowing blue machine in the heart of Castle Markov. Is this machine connected to the Blue Lanterns - and is Brion planning on resurrecting his sister? His current crazy and violent behaviour is, according to Didio, a continuation of Deathstroke's claim that he drugged Tara and is mixed up with the Markovs getting their powers. In other words, Brion is currently going down the same road to madness that Tara did - but why? and how? and who or what is causing it? I've always thought it strange that Geo-Force said in JLA that Deathstroke gave him Terra's powers - how could he do this? Deathstroke's not a scientist. But he likely did have connections with the woman whose treatment sparked powers in both GF and Terra.