I just did this last week. I had dreads that were about 1.5 years old, and very developed. Not just developed, but I used a felting needle a lot and my brother spent many days using a crochet needle to get them nice and tight.
I cut the bottom couple of inches off and me and my husband spent a week soaking dreads in conditioner and picking them out with forks and flea combs. I stabbed myself in the fingers and thumb so many times they were raw, yikes!
I used generic Nexxus, generic Redken Extreme, and Ionic condioner from Sally's. I don't necessarily recommend these; I KNOW there has to be something more slippery. They worked well enough, though. I just didn't take time to research it much, I was ready for them to be out.
I cut them off to just on top of the shoulder, but after they combed out some of my hair was down to my sternum and lower. I can't believe how much my hair grew while in dreads! I now have hair that is collar bone length, and it's thinner at the ends than the roots, but I started out with very thick hair, so my hair mostly looks other women's hair. It really doesn't look very damaged or anything. I may get more cut off the ends, to just above shoulder length as I liked that length on myself before. I'm just waiting to see how it recovers from the dreading and then the removing process.
It's funny that the ladies at Sally's kept telling me that it can't be done, that you HAVE to cut dreadlocks out. I kept saying..."I've seen it done, I'm doing it right now, they're combing out as I'm talking to you on the phone..." I keep wanting to go back and show them.