Charlie -
I am not an expert on the Supra, but the Tige' I own uses a moveable wake plate called Taps. This is a device used on the Tige' boats to shape the wakes from small to large to create versatility. You can adjust it to ski or wakeboard making the boat a little more flexible for all boaters in your family.
As far as long term to the transom, there is no issue, the boat is built to be used this way. Look at the stress a Outboard or I/O drive will put on a transom, and the wakeplate really is not a lot of stress. The porpoising is due to hull design made to allow this versatile wake change. The hull is in a bow to stern convex shape. At higher speeds this puts the boat into a rocking position when it is lifted on plane. By lowering the wakeplate it acts like a plane's aileron to counteract the rocking motion, and allow the boat to create a smaller/softer wake for water skiing.
Look up the Tige' web page at
www.tige.com. This should let you see the physics and thought process involved. It is current technology which makes a boat a little more versatile. Take a look, it does work, and the concerns you have, really shouldn't be a second thought.