Agree with Matt also, my Tom's set on a 174 flopped side to side so badly just when rolling the sled on it's side to adjust something, it was silly. Unless T-Motion is locked out, it needs the springs to stabilize and center the skid. It was so bad that I had a hard time adjusting the track on the trail. We had to get ALL the snow out of it, make sure the skis were level, then hold the rear bumper to check adjustment.I agree what Matte said about Tom's. I have run that set up for years and it blows me away how much the track pivots. Maybe it's because it eliminates the torsion springs but regardless if you grab my rear bumper on either of my 850's when the sled is on flat concrete the bumper can rotate quite a bit with zero track movement. I have a hard time believing this doesn't make a sled more squirrely. However, if you have a very high skill level this can be preferred.
For example, I used to Wakeboard professionally and rode with no fins. I never taught people to ride with no fins. Most people will never make it to that skill level. Unfortunately novice riders always want to imitate pro level set ups.
That being said, I think you can do anything with the T motion. It doesn't "need" to be deleted to get an 850 to do anything. You just aren't that good of a rider if you have to delete it to "get" the sled to do anything. This is why I think an Axys is an easier sled to ride because it's much more predictable to ride. I still prefer riding a Ski Doo with T motion with the E motion set up. I just think the guys on this forum that spout you "need" to delete it aren't very good riders. Then again I have yet to meet someone off this forum that I would consider an expert rider :face-icon-small-con
T-Motion should be an option from Skidoo,they have already made all the parts to replace it other than on a 174/175.