Well, Ajahn Chah is at least one lifetime more experienced a meditator than I am and so I'll have to just give you my perspective of his view.

From what I understand of the Thai forest tradition, they believe that the method of practice the Buddha taught was the gradual training outlined in several early suttas, which culminates with the method of meditation adumbrated in the anapansati sutta. Unfortunately, every step of these step-by-step meditation instructions are defined differently even by each Thai forest Ajahn.

• Interpretations of step 1: Build concentration by doing a task which is the equivalent of counting breaths / Have awareness of every conscious breath you take / Learn to feel the energetic differences caused by different types of breathing / Cultivate vicara etc.
• Step 2: See the breath start to finish at the anapana spot / See the breath as a whole / Become mindful of your whole body breathing etc.
• Step 3: Relax the whole body / Spread piti throughout the body by directing your awareness / Allow most of your senses to begin to switch off etc.

And that is just the first quarter of the process. Nonetheless, I'm fairly sure Ajahn Chah interpreted it as a process of mindfulness of a relatively open awareness of the breath leading to a nimitta which reveals the citta directly after all of the senses have switched off, which this leads to a form of the jhanas that the Buddha discovered. Thai forest monks spend a year in contemplation, walking the countryside alone, and often do six month retreats. I'm open to the idea that the interpretation of the sutta that Ajahn Chah has reveals certain contemplative possibilities, but I would think that few people experience them themselves. It is quite controversial to interpret this sutta this way. A Mahasi monk who has no experience or interest in samatha-jhana or anapanasati would interpret the sutta as instruction to pay attention to the breath, go through the jhanas, and to then either investigate the three characteristics, cultivate the factors of awakening, or recall all of ones past lives. They would probably interpret some of the final steps of Ajahn Chah's interpretation of the sutta as entry into the fourth lokuttara jhana.

All of this should help explain the problems in talking about stuff like this. Experiences might be supermundane, mundane, or pathological, and could mean anything, or even nothing. Given this disclaimer, most of my thoughts about path of mental maturation would have to centre around a discussion of possible progressions through the dukkha nanas.