Different tai chi lineages and masters interpret chi differently. Some put more emphasis on it, some put less, a few frown upon it, as if a mentioning of chi diminishes tai chi's rightful place as a martial art. In my opinion, there will be no tai chi without a proper activation of chi. And the best chi interpretation in the literature is by late master Wu Tunan (吴图南). In his life time he published an important article on tai chi's interpretation chi and the internal personal sensation (feeling) of chi generation. This article has been reprinted in two publications by his different students. It is not that famous masters were withholding important information, it is that it demands an informed reading of such texts, plus actual training experience under an informed training method.
The following extract is the core of master Wu Tunan's teaching on chi kung (as used in tai chi). The original Chinese is posted here for those who can read the language. After that I shall explain the gist of Wu's teaching using the English language, for the majority of my readers.
The gist of the matter (underlined part) is through the activation of chi, our body's chi activated tissues will be "raised up" or "expanded". The primarily focus is tissues around our joints, in particular our shoulder and pelvic joints. Only with chi activated tissues around our joints can our muscles be connected and our body structure strengthened. And only with chi activated tissues around our joints can joint rotation (silk reeling) develop meaningful training results. Such chi connectedness will eventually reach the extremities our body. In pushing hands the internal sensation and reach the inside of the your opponent's (training partner's) body.
In short, the focus is on muscles and body structure, instead of on chakras. The latter is the primarily focus for meditators, which will necessarily be the subject matter of another post in future.