Any solution that involves growing things is not going to be instant so a hedge on stilts doesn't have to be bought in ready made and grown. It can be bought young, trained up and grown on.
The advice about trees for perspective at different heights and distances is sound and will make the garden interesting but also take time to grow. A lot depends on how much budget is available and how much patience. No point having a 10 year plan if the owner is not planning to stay more than 5 and needs instant privacy. In that case, a pergola will serve best.