I think the Dhamma is very deep and very hard to understand even intellectually. The Tilakkhana is not at all easy to comprehend, and most of us have only the very shallow level of intellectual understanding, let alone the level got from practice. We struggle with forming the idea of what anicca, dukkha and anatta is, so I think it is a mistake to think that we have any 'correct' understanding. It can lead us the wrong way.
We do have our conventional ideas about these and they may well be distinguished in our minds. But these conventional ideas do not lead to the understanding of the actual. Rather once we understand the actual characteristics of dhammas, our understanding of these conventional concepts will be different. As of now however, we are mostly just playing with "ideas".
Impermanence, Suffering and Non-self are characteristics of dhammas of which we still do not understand at all. We have at best a very vague understanding of matter, feelings, perception, consciousness and formations. Rupa for example, is so different from what most of us understand as 'matter'. Mind which is much more subtle is completely different. Feeling is different from perception and seeing is different from hearing. And this is why the first real understanding occurs when mind and matter is distinguished at the first vipassananana.
It is true that that which is ultimate must reflect one way or another in conventional reality. But so far our understanding of conventional reality is from the standpoint of ignorance (of dhammas). This is where Science and any modern enthusiast of Buddha Dhamma are at. So I doubt that the popularity of Buddhism and the apparent agreement between science and Dhamma should be taken as sign of the "growth" of the Sasana. For example, would science ever arrive at the conclusion that there are 28 rupas? No, I think that science is going in a totally different direction, one that is reliant upon concepts to explain other concepts and not one that will arrive at an understanding of even a *single* dhamma.
In other words, who so ever sees a parallel and possible merging of science and Dhamma may in fact be far from having an understanding of the Buddha's teachings, enough to be moving in the right direction. Better to be patient with the realization that our understanding of Dhamma is very weak, better to know also that the goal is to develop our own understanding and not think too much about how other's are doing and how to encourage them. Worse still to act on the idea about 'groups' and 'peoples', which I think to be ultimately nothing but a game centered on 'self'.
The Sasana stands and falls with reference not to the number of people going around calling themselves "Buddhist". Nor is it to the fact that the 'Books' are intact, which I think will last many thousands of years more. Scholars and other curious individuals will forever exist and lobha will in the name of saddha, preserve in gold or on CD the Teachings 'forever'. These are the forces which are in fact opposed to the one that actually maintains the Sasana, namely "understanding". It may be the single individual who 'understands correctly' the Dhamma in the last 500 years of the 5000 predicted who takes the Sasana along with him at his death, while millions still go on living calling themselves Buddhists, who knows?
Hope there has been some food for thought here.