it would still need to load each world like with the portal
that your BC engines not accepting the cells has nothing to do with ic² since it's space toads machine and he have to add it so it can take lava from the cells so if you want it like that go to his forum and not here
So yea. i know there's the Magnitizer but how about if you have the time (and maybe for those that don't have metal boots for some reason) an Elevator! so you basicly create a bunch of "elevator" blocks and maybe an motor which you can place next to an iron fence? (magnitizer needed ofc to make it work) and then you can build an custom size platform (ofc not too big.. that would cause severe lag or worse) and now for the question. how do we make it go up/down? well just apply some redstone current to make it go down (redstone on the magnitizer) and turn the current of to go up. and now if you want to have perhaps multiple floors just make an small redstone circut with pistons which will stop the platform in it's decent (or up)
the rest like Energy consumption, Crafting recipe we can let Alblaka decide.