I really don't think the danger of modern trials keeps young riders away.
Look at downhill mountain biking - hugely popular here in NZ. Take a look at the tracks being built all over the place, full of "do or die" drop offs and gaps with loads of teenagers bombing down them having a great time. Plenty of older guys too and lots of injuries. People love it and lots of council funding is going into track building and maintenance.
Show most kids a slow, technical, snotty trials section and it just looks boring. If they give it a try, they realize that it's going to take a lot of practice to get good and even then it won't really impress their mates or (more importantly) the opposite sex.
Trials is in a difficult position I believe because it probably needs to be flashy and extreme to attract young riders but it's so difficult to get to that level that many will give up.
I don't know what the answer is but times have changed and I don't think keeping the sport at a level that old guys enjoy will help secure it's future.