I've been toying with a weird view of jump space. Instead of an open 2d mapping of space each sector (or cluster) is mapped on an icosahedral map. The result is a 'closed' sector (at least as far as jump drives are concerned.) The stars are generally nearby in normal space but their 3d positions don't matter. The map portrays their positions in jump space. So normally a ship can't leave the cluster anymore than a ground car can leave its planet.
Each cluster can have one or gateway hexes (usually with a world present.) In these hexes a ship's jump drive can send it to another cluster. This may require a certain level of jump drive.
The gateway hexes can link clusters that are very far apart in space. A cluster near the galactic core could be adjacent to one in the galactic halo. That lets the characters access wildly different areas of space without spending years in transit though they certainly can spend years traveling.
The advantage is none of this really changes the basic assumptions of Traveller (communication at speed of travel.)
Actually, because of the discontinuity of J-Space and N-Space, it's possible that some systems might be only a few light weeks apart, but several times that by jump, allowing for dedicated radio comm "bridges", and depending upon how one defines a "system", it's possible that one might even have systems only a few light days apart (and thus within N-space reach).
Keep in mind: Neptune's a mere 250 Light Minutes out from Sol, and the Ooort is 41-80 Light-weeks (0.8-1.5 LY). Many star systems have far companions in the 1-10 L-Wk range. The cost of going "slow" 10 LW would be a peak of about 75PSL, for about 13.33 weeks, plus acceleration. 6G ships could do it in about 16 weeks - 4 months, or 24% fuel at CT-HG rates.
It's a wicked way to have some interesting topologies in a non-correspondent system. (It's also an idea stolen from a Starfire story/campaign... the two systems were nowhere close on the warp-line maps, but were very close, a few light weeks, in N-space, so the aggressive xenophobes observed that they were not alone, and snuck up upon the major race... it's from an early issue of Nexus Magazine.)
Also, if one has the T5 Icosahedral world maps, one can "nest" them easily enough, especially if one prints them with the same size hexes on overhead transparencies; the triangles make it easier to line it up the "inner map" under the outer map for any given triangle pair.
