To echo what others have said, it's not necessary to turn off WM. There are plenty of options available to use for attacking on the move that should allow enough time to pass to allow you to be stationary when attacking. Feint, Blunt Arrow, Bloodletter, Rain of Death, refreshing Straight Shot. Just using Feint, Bloodletter, and Blunt Arrow as on the go attacks will most definitely allow enough time to pass to allow you to be stationary when going back to your regular rotation.

On topic: If Swiftcast's cooldown is reduced I feel that it should only be reduced to 45 secs, kind of meeting you halfway on what you'd like versus the current cooldown, but I really don't feel that it's necessary to reduce the cooldown and as others have stated, it seems that balance issues could come into play if the cooldown was reduced. I think a better option would be to have something like Spell Speed have an effect on the cooldown. The more SS you have the more of a reduction that you would see to the cooldown time.