Neat idea. Probably not cost effective.
We could do some math.
BoatTest.com has results of some in water testing.
20' Bayliner with Merc 150 and three different props.
In the 32 mph range (where I usually ski) they measured 7.8, 7.7, and 7.1 gallons per hour.
Since I got the Mastercraft I've run it 1600 hours and damaged two props.
So, 800 hours per prop; 0.7 GPH less fuel flow; I'm paying about $3.10 a gallon for mid-grade (not going to join the octane discussion just yet); that comes to $1,736. Really less since quite a few of those hours are at idle.
Need to have numbers for a DD inboard since I'm not going to switch to a Bayliner, but this gives me some perspective.
If they can offer it substantially under $2,000 I might start to be interested.
Moot point so far with nothing offered for inboards below 25" as mentioned above.
Also I liked @Thager's "sceptic" comment.