X3: Reunion was originally scheduled to be released in August of 2007 (and the LGP product page still reflects this earlier target date), but that clearly didn't happen. Since July we've finally seen a new beta release of X3 as part of Linux Game Publishing's private beta program. There was a month-long server outage with Linux Game Publishing which complicated the situation.
The CEO of Linux Game Publishing, Michael Simms, had yesterday released the 18th beta for X3: Reunion to its closed testing community. This beta release is supposed to be "pretty much bug free", but there are still some outstanding issues they hope to resolve before the 19th beta or prior to going gold.
As it looks like the development on this strategy game is finally winding down, we'll hopefully see this release before year's end. No official announcement has been made, but with it now being the end of September and still having possibly another beta to go, we would suspect X3: Reunion for Linux will finally make it out towards the end of October or November. Once they have their finalized copy, it will take a few weeks for manufacturing.