I will attempt to pass on my limited knowledge about sledding.
The sled is a steel plate, approx 3m wide and 2.5 to 3m long, not sure how thick, looks about 25mm.It has a small v section in the middle of the underside of the sled, and some tynes as well on the outer edge of the v, similiar to what is on a grader. There are also other variations and applications which I will try and explain later.
The sled is dug under the track, by hand, or by digging out the sleeper bays with a machine and then it is pushed under the track.They have been using a sled to remove some mud holes along with the gang that does there scratch outs.They have been pulling it with a loader.
Dry sledding is where the sled is dug under the track, and steel wire ropes are attached to lugs on the front sides of the sled, the ropes are then attached to a spreader bar that sits nearly on top of the rail and then two more ropes are attached to the towing implement, you then drag it forward, and the crib ballast falls behind the sled, and lifts the track by 50 to 100mm, the v on the sled cuts a furrow so that the sleepers don't get centre bound, and the tynes break up the base and allow the mud to go down wards.
You then run a ballast train and tamp, and you get a section of new ballast on top and the muddy/dirty ballast underneath.
Wet sledding is where you flood the track first and you have a bigger section of clean ballast , before filling the cribs and tamping.
It wont help with the wrecked formation, as it will not get down that deep, it only runs under the sleeper. The wrecked formation was caused by the FLIPPER or DUCK BILL attachment on the excavators, digging too deep into the formation.Note; Side Insertion was not the cause, it has been used for many years around the world, by both excavators and Tie Gangs.
They will have some problems, Sledding of Concrete sleepers will cause the sleepers to Bunch at the start of the sledding run and at the END of the sledding run, they will also break some, especially those that have been flogging in the mud holes, as timber and steel flex, concrete won't.And there concrete sleepers use the Fast Clip fastening system which is not as strong as the E-Clip or Fist Fastening used in QLD
There are other types of sleds as well, the ones used to rip up the line at Marree, check you tube for that video.
Also there is grainy vision on youtube, called Mighty Steel Goonyella at the 11.5 minute mark, this shows a sled on initial construction, which I think looks like two sleds connected together, with the back one, pushing the ballast out towards the shoulders.
I have a video called Just Australian Trains and that has I think the same vision.
Also Roberts construction used to wet sled in QLD in the 70's whilst construction, of the Coal Lines, it certainly saved the tampers lifting the track by 100mm at a time, on one section they constructed 148km in 6 months, with there SUM 100 Track Layer and 1 x 06 Tamper and 1 x Mark 3 Tamper as well, but no ballast could be run for 3 months, until they laid past the ballast pit, so sledding was the only way to meet the deadlines.
Also QR have a sled car, I saw it at Yukan a couple of years ago, it looks like RailCorp Plough Van (New One) it has a sled underneath and a set of lifting clamps like a tamper as well.
RailCorp still have a couple of sleds, but they don't use them anymore due to safety concerns, (wire ropes breaking etc)
I have seen sledded track on the Nth Shore line in Sydney and you could clearly see where the muddy section was and the new section of ballast was on top.
If they sled, and maybe use the Shoulder ballast cleaner straight behind, they may have some success, but sledding alone will only give you a lift and some clean ballast, the underlying problem is still there.
I hope this helps.