counting equal steps to 2 motors has been perfected since the first i3 printer came about. This is no problem. The benefits of this conversion will be speed and strength without artifacts in the print from heavy axes being slung back and forth, to and froe. It is the difference between pushing or pulling depending on which way you are going vs. pushing AND pulling in each direction. I ran 2 motors for my Y axis on my Black Widow printer with the big heavy 400x250 heatbed with 3mm borosilicate glass plate. It works amazing. no more skipped steps and I was able to raise the print speed as well. 2 motors on an axis directly translates into 2x holding torque on that axis.

Another great place for this conversion would be if you had a 12v printer and wanted to run the silent drivers in stealthchop. a second motor and driver on a given axis would go a long way towards correcting for the lost holding torque.