I really like the idea of jump gates. I envision this would be similar to Babylon 5, where you have both ships without a jump dive that solely use the jump gates, and other ships with jump drives like regular Traveller. I would change one thing, I would require a jump gate at both ends (paired). These are built by large "explorer ships" (like the Cortez) that have their own jump drives and carry the components to a new system.
To simplify things for my own campaign, I would overlay the government owned jump gate network on the X-boat network. I would also have jump gates work like jump drives, every jump still takes one week. The jump gates would be located just beyond the 100 diameter limit (from the world or sun). I would limit my jump gates to a maximum jump-4 (like X-boats) and set the arbitrary maximum ship size to 50,000 dTons. Most big military ships would have their own jump drive (for tactical and strategic flexibility), but the Hadrian Class Battle Riders could move from system to system using the gates. Ships with jump drives could still use the gates, which would make sense for faster travel (i.e. a jump-2 far trader could more rapidly cross the sub-sector using jump-4 gates).
My jump gates would built like a space station with jump drives for a jump-4, 50,000 dTon ship. The only difference is that it doesn't move. It just has station keeping thrusters.
The jump gates themselves would be look exactly the same as the Babylon 5 ones (since there is already good imagery for them). They would have a control centre that also acted as the station for the X-boats. They would have a large repulsor bay (to be used as a tractor beam) for pulling in the x-boats for refuelling. These control centres would also have large transmitters for sharing the data from the X-boats. The jump gates would have significant defences due to their high value and the fact they would be a target in any conflict.
One key component is there would be a series of tankers constantly shuttling fuel from the gas giant or other source of hydrogen. I would retcon that all X-boat network worlds have gas giants. The gates would have some huge spherical hydrogen tanks attached to them.
I like the concept of jump gates being like the Panama Canal or Suez Canal. In keeping with that idea, the cost to transit them would be based on your size. I still have to work out what the cost would be, but it would be equivalent to the refined hydrogen you use, plus a percentage of the amortised cost of the jump gate.
This would definitely increase the flow of traffic along the X-boat routes. I can see high population worlds off the X-boat routes to pay the cost to have their own jump gates installed to connect them to the X-boat network. This would not be consistent, as some worlds would not be able to afford the cost.
I recognise this would change the economics of the Traveller universe, but my campaigns have never revolved around GDP of worlds. My campaigns revolve around cool adventures. Taking jump gates from system to system until the PCs leave and go off to a remote world just sounds like more fun.