The only successful one design competition in the world for sailplanes that I know of is the Schweizer 1-26 Championships. I will say that it is a lot of fun setting out on task with a group all in the exact same glider. Differences in pilots get sorted out very quickly.

The one design concept for 1-26's came about due to a lot of effort in the early days by Schweizer to establish the Championships as well as supporting the early 1-26 Association. I think any future successful one design contest will also require major manufacturer support or a strong type club to get the ball rolling.