It's a bit ridiculous to expect scientists to create a timeline for technological breakthroughs. By definition, the breakthroughs haven't happened yet, and there's really no way to tell when they'll happen. Anti-gravity, for instance, may be invented in 2 days, 200 years, 2,000 years, or never.
The corollary is that its impossible for us to know if we're experiencing technological stagnation. We're obviously experiencing some
progress, but it's impossible to know if human civilization is evolving at a slow pace, a moderate pace, or a fast pace. We've never met any other species with advanced civilizations, and we don't have access to parallel realities to act as a point of reference.