Im not sure if this idea will fit into Ic2, but Im not know if its should to be addon becouse it will change the mod completely.
making machine is really boring, and once you will finish making them, you will not have what to do with them next exept adding upgrades like overcloackers and automating them.
my idea is to make that the machines will be made in a way, that you will make in a crafting table the parts, and then build in world the machine, and to upgrade it you will change its component into better tier.
for example, an electric furnace will need you to place a machine base,machine walls, furnace top and front ( 
) , and inside it few components like redstone controlled/GUI controled( 
/ 
), power connection (better tier for higher current exeption 
/ 
... ), motherboard (the higher tier the more options you will have at the GUI), and the better the components will be the machine will be better and more high tech (faster, exepting higher current...). right clicking with a component will add it, right clicking with a wrench on a component will remove it, shift right clicking on the machine will break the machine into its components, and just bricking the machine with any kind of tool will destroy some of the components.
the components will be crafted in a crafting table, but placed inside the machine in-world
for autocrafting thouse machines there may be a machine that you will put the components in it, and you will modify it how to make the machine, and it will auto make it (using eu) every time its will have all the components its need
like this, players will be able to modify their machines a bit, and to upgrade them in a diffrent way (adding/upgrading a component)