Thom Denholm brings up the Imperium Map Expanded (from the Classic Traveller CD-ROM) here: http://boardgamegeek.com/thread/531814/major-version-differe...
The front page mentions an "Expanding Imperium" article in Dragon 27.
Hmm... this sounds like we need to investigate!
To summarize the Dragon article;
it proposes a variant where a second copy of the Imperium game is used to add more star systems to the game. The second map is placed beside the original, and the Imperial "upper" end connects to the "lower" end on the second map, while the Terran "lower" end, connects to the "upper" end on the second map. Essentially a copy of your opponent's space is made adjacent to you, ready for exploration. You can then meet your opponent half way through the second map.
To dispel any confusion: The warp lanes leading out of the map from the uppermost systems of Dingir, Kirunir, Gashidda and Ishkur now lead to the bottom of the second map and to Kagukhasaggan 2, Ember 2, Dismal 2, and Forlorn 2 respectively. In a similar way the Terrans can reach the upper edge of the second map (Kagukhasaggan to Dingir 2 etc)
A heavy focus in this variant is exploration. Apart from the four pairs of warp lanes leading between map boards no system and warp lane is discovered when the game starts. You'll need to make a note or otherwise mark systems as they're explored and warp lanes as they're chartered.
Systems are randomized, meaning that on the second map you aren't guaranteed that Sol 2 will be a primary system or that Sirius 2 a tertiary, or indeed that there will be any tertiary systems at all. Also, systems might be inhabited, and the locals might be hostile to your side!
To reinforce this theme of exploration, the game starts at peace, and remains so until either player declares war. (You might still need fleets to subdue the local defenses of any "natives"). Once war starts, there's no time to continue exploration - you're limited to the lanes and worlds you have found that far! Essentially the idea seems to be that between each standard Imperium campaign war your map of explored space grows: in each subsequent war there's more to fight over.
There are additional optional rules to add Alien Artifacts to what you can find when you're out exploring. These add bonuses to various attack and defense values or add completely new capabilities much like Technologies do in other space empire games. Examples include Transport Beams, Nova Trigger Bombs and Cloaking Devices. The article does note that the inherent randomness of these finds could conceivably favor only one side, and thus contribute to an especially unbalanced game.
There are even whackier optional rules (Rogue Cities that are essentially worlds that move on their own, Berserker Ships that kill everything in their path and need to be stopped) too.
The variant does add an equal amount of new space to each of the two players, and I like how it integrates the existing idea of peace between wars with continued exploration. It is, of course, mostly random.
What it does not do, however, is add anything specific to the Traveller universe (and the Imperium Map Expanded) - the additions don't sound and feel very Traveller-specific (at least not to me).
If we're looking for a set of variant rules that can be applied to the Imperium Map Expanded this ain't it. (Now I mean Traveller specific rules additions such as: more Imperial Governors possibly AI controlled, introducing the Vega Polity - Vega lies just "above" Gashidda and in the Traveller universe played an important part in the "historical" development of the conflict portrayed by the game, i.e. the series of interstellar wars that led to the defeat of the Third Imperium and to the Rule of Man).
The core game of Imperium is much about economics, diplomacy and the Governor's relation to the Emperor. These concepts are clearly not what motivated Roberto Camino when he wrote that article.