I think IC² (without additional mods) currently lacks a long term endgame target. Once you have your quantum suit and a few miners going, there isn't much to do except for hording insane amounts of resources, but there is nothing to spend them on. As one idea of such possible endgame targets I suggest to implement an item I call "Void Sphere".
The initial machine you craft is the Void Machine. It requires a huge amount of resources and once placed, it needs to be filled with 1 obsidian, 25 diamonds, 16x stacks refined iron, and several stacks of Redstone (the idea here is to be very expensive). Once filled, the machine needs to be activated by supplying 1,000,000,000 EU (one billion). The moment everything is provided, the machine causes an explosion similar to a nuke, except that the machine itself survives unharmed and all items including the EU have been consumed to produce a single Void Sphere.
This void sphere is an item that can be carried around and can either be used in the battery slot, which will provide up to 128 EU/t but it will not loose energy in the process (read: it has unlimited EU stored) and can be used in any machine that accepts medium power. Alternatively it can be used to activate any machine and power it for one operation similar to redstone, just that you simply need to right-click the machine while holding the Void Sphere. This includes teleporters, which will then be activated and teleport you immediately. In all cases the Void Sphere is never used up, that is: it provides unlimited power.
While this is definitely an extremely powerful item, the resources and EU required brings this down to a point where you can say: if you are capable of providing the base material and 1.000.000.000 EU, you are at a point in the game, where resources and EU have become meaningless anyway. At that point you basically have unlimited power and resources already, the only difference to the void sphere is that you need to actually wire the machines first. So at this point in the game, even if the Void Sphere is very powerful, it is just a slight upgrade to what you already have.
Quick math: let's assume you are capable of producing 1,000 EU/t with stable power generation (that is no CASUC or similar) - which is an almost insane value on its own - you would still have to let that run for 50,000 seconds (about 14 hours) to produce a single Void Sphere. The same amount of power for example is enough to power 2000 diamond/OV miners, or to produce 1000 UU-matter (without using scrap). If you are at that point in the game, you basically have unlimited power, the Void Sphere then is just this fact condensed into a single item.
The other idea beside giving you unlimited energy is that it is mobile. So you are free to explore the world and can carry your power generation right in your pocket. That combined with a teleporter allows you to travel back and forth between your current location and your base at any time, so there is no way for you to get lost, no matter how far you are away from home.