That's the real taiji.
This discussion is one that comes up every few months. To me "internal" and "external" are just lenses we can put on our training. Just like sometimes we may focus on throwing skills and other times we may focus on striking skills, or one day work upper body strength and another day work legs... I can make my cross more powerful by doing strength training and hitting the heavy bag and I can make it more powerful by working on my body mechanics and breath control. To optimize I have to do all of it. Every martial artist works on all of these. The only real differences come down to proportion.
Usually we study "external" styles at my school (shaolin, longfist, eagle claw), today we worked taiji push hands. The skills are the same...just in the push hands, we work with a speed and a rule set that emphasizes structure, instead of one that allows speed, power, and adaptability to compensate for weak structure. Ultimately we have to have it all to really reach a high level.
To me the internal/external labels make much more sense as training approaches than as style designations...Shaolin kung fu is the classic example of "external," yet without internal work, it isn't real Shaolin. And, as Bawang will point out
, "real taiji lifts weights."
Looking at the forms and jibengong, it's easy to see why taiji is considered internal, but after studying tongbeiquan for three months, I really couldn't tell you why it's considered an "internal" style...probably just to feel special.
But yeah..every martial artist should train speed and power, and every martial artist should train mechanics...so...?