Wouter, your "ideal path" is 6 YEARS too late. In the US, kids can start on Optis at age 6 (and I can't find a rule that says they can't start earlier):
And I really don't know why anyone wants to compete with the 29er. I've been to youth regattas with hundreds of boats and no 29ers. It's just not a big class here. RYA alluded to that as well in their submission.
A kid can sail an Opti from age 6 to 16. Most stop sooner because they get too big (or bored). The next boat up is either a Laser (as mentioned above, several rigging options) for singlehanders, or a Club 420 for doublehanders.
The Laser can be sailed into retirement. The Club 420 can be sailed in high school and college programs. They both have huge fleets.
Having said all of that, I maintain that it's not about the boats. These classes are the accepted boats at most yacht clubs, the infrastucture, convenience, and sheer numbers of which is quite formidable.
EDIT: More to the point of why the boat doesn't matter: there have been a ton of new boats introduced that have flopped (Escape comes to mind). Look at the number of models on Vanguard's website. The "establishment" of the clubs is the real strength. And, say what you want about Hobie 16s, they are still far and away the most popular racing catamaran in the world.
