This has got me thinking, once again, that one of these days, we should do some sort of starship design contests or collaborations, like they used to have at the Subspace Coms.
I wonder what different designs people would come up with, or what the final design would look like, if we took the best design elements artists and designers could think of, and used them to create a new ship, such as a future Enterprise beyond even the Universe class.
For example, I would suggest: what if a starship contemporary of the Enterprise-Z didn't carry just one of those energy sources (which I assume is either a compact quantum singularity, or a Zero Point Energy reactor similar to those used by the Ancients in Stargate), but carried a number of them, perhaps either placed throughout the ship, or in a single engineering room. A ship the size of Manhattan, or similar to Atlantis, for example could have a three. I know that it wouldn't be in so innocuous looking a place though, given how critical it would be.
If we are talking about the propulsion system though, then I doubt they could be that small. Thin, long, and stretched throughout the ship, probably, but still taking up a sizable proportion of the ship, so that it has enough coverage to do what it needs to do to the ship, or the space surrounding her. That is not to say that they might not be compact compared to the original Enterprise though.