One of the basic principals of good ride and handling is to minimize unsprung weight. Since mounting the rack on the axle adds weight it just seems like the wrong move.
The only piece of the existing system that is both unsprung and removed in this conversion, is the tie-rod. I don't know what it weighs compared to the rack and pinion, but I'm sure it doesn't weigh as much.
If you read the other threads you know there is a kit to put a rack and pinion on the axle so someone has worked out the details and made it easy to do.
