For knitted sensors and interfaces, it will be great if there were also knitted cables. So, I tried it!
By using Spool knitting tool (Strickliesel in German), you can make a knitted tube easily. For more easier and faster solution, you can also use automatic Knitting Mill (Strickmühle). This tube is an isolation layer for the knitted cable. Insert conductive thread inside the tube, connect the each end to conductive fabric and poppers.
The result is quite satisfying. It is stretchy, highly conductive (depending on the kind of conductive thread used in the middle), and it is well isolated.

First, make a knitted tube using Spool knitting tool. If you have an automatic Knitting mills, it is much faster. I made it about 20 cm long each.

All the other materials needed is following:
-conductive thread (tube length + 20cm)
-conductive fabric (1cm*1cm)
-1 set (male/female) of poppers (10mm ∅ in this example)
-normal thread (not necessary)
-needles (thick yarn needle maybe handy for threading the tube)

Thread the conductive thread through the knitted tube. It makes it easy to use thick yarn needle to do this.

Add a small piece (5mm*10mm) of conductive fabric on each end. Connect the end of the conductive thread to fabric by sewing through it.

Pull the yarn on the each end of the tube to close it tight and make a knot. Cut off the extra yarn.

Fix poppers on each end, placing on the conductive fabric pieces to get the connection. In this example, I used male and female poppers on each side. This will differ depending on your project plan. It can be other kind of conductive connecters as well.

Here is the Isolation test. I am twisting and pulling two cables together to see if you get a short circuit.

These cables are used in the knitted interface project (still in process, post coming soon). It connects knitted sensors to the microcontroller (lilypad) circuit (inside the circular knitted pocket).