My reasons for not are as follows
Why??? whats it gaining you. It doesn't get rid of bumper steer it may well add bump steer into the front end that you didn't have before.
The sliding shaft is going to send a lot of shock and vibrations up the shaft and into your hands now that its location is un-sprung and has no shock suppression. Hit a bump and its tire and what ever little absorption the slide joint offers then your hands.
Since the rack is on the axle, and moves with the axle, there should not be any bumpsteer.
Your point about bumps in the road being transmitted up the steering shaft to the steering wheel seems like a definite negative. No matter how smooth the telescopic action of the steering shaft works, there is still going to be vibration transmitted.
