I've always believed that as the GTVA's technology advanced they would find new and better (or worse, depending on how you look at it) ways to use and manipulate subspace.
Among other things, a "sub-subspace" might offer even faster travel within "normal subspace". A jump from Delta S. to Sol takes approximately 10 minutes which are spent inside a subspace corridor. Imagine entering an underlying layer of "sub-subspace" to go even faster. Yeah, I know, it's a wild and ridiculous sounding idea, but I never said I was a scientist.

Another thing subspace could be used for is wanton destruction. If the GTVA could somehow harness the power of subspace in such a way that they could open a subspace jump node by remote, at a predetermined location, it could cause chaos in enemy lines. Imagine a specially modified Hades warship, equipped with some impressive, top secret subspace device that could rip open subspace wherever it wanted to. Suppose it targeted the center of mass of an Orion-class destroyer and opened a subspace node right in the middle of it. A subspace node no different than those ships use to commence regular jumps, only without a ship jumping into it. If used correctly, it could be more devestating than all the beam weapons on the Colossus combined. Or, if you wanted to go for superdestruction, how about opening multiple doors to subspace
inside a star. It's quite possible it would substantually alter the mass of the star in question, maybe even going as far as to destablize it. The impilcations of such a horrendous event would be catastrophic for the inhabitants of the system.
Oh, and on a side note, I find this

to be quite disgusting.
Just kidding.