I can only make my observations based upon game lore and canon, and as of the last information we had the Wolf Empire has its sights set on the Lyran Commonwealth - up to the Khan declaring himself Archon (and then backing somewhat down, but his intentions are clear) - and nothing showing any desire to merge with the FWL. Hell, why would they want to? They already killed the Captain-General, shattered their main forces, and nearly caused the whole thing to fall apart again. They wouldn't become part of the FWL, they'd ****** conquer it.