Paul there have been several ideas that have been tried.
Not so much going aground but some full keel boats with tall bulkhead will bold a 4x4 to each side with a flat pad on the bottom so the boat can dry out at low tide.
It gives the boat a couple of legs to prevent it from tipping over.
There have been some commercial floating water-wings that you put under the bow or stern then inflate to lift your boat up. Saw them for sale never saw then used.
The old standby of course is a backhoe. It can be used to dig a trench then to push the boat while a tug pulls. I've seen the video of that process.
The first thing someone does when aground is to use the dinghy to run an anchor out to seaward.
That keeps the boat from being washed up higher on the beach.
Sometime with constant tension kept on that line the boat will work free.
Your idea might help in conjunction with the seaward anchor. It is the kind of idea where you you have to evaluate the situation and go home to get the right gear. It is highly unlikely you would be willing to carry the proper timber etc in the unlikely event you would need it and that the material you brought would be just right for the circumstances.
If you have a hydraulically operated center board then of course the solution might be easy in a soft grounding.
Let me know how you would have used your method to float this boat?