Not side by side, but this feature is already in Ultimate.

Just Right click on the thumbnail and select Softproof.
When you get the big picture up. right click on that and you can pop back and forth from Original to Softproof and back.

Also bear in mind that Softproof just compares the monitor profile with the printer profile... not really worth so much emphasis unless your monitor is really profiled very well.
Always better to make a test print and not rely on Softproof.

Fred