One) it is not necessary to be mechaven during chazaras hashatz. We are not being yotzeh with the shatz.
Two) tekios are infinitly more confusing and harder to follow.
1. If we're going with that assumption, then we should just skip the whole thing.
2. I was thinking more along the lines of, just like people can look in the Sidur for Chazaras Hashatz, so can they do for Tekios if they wish, (that's what I do).
When did it start?
There are countless letters from the Previous Rebbe, at least as early as the 1920s requesting that it be instituted not just in Chabad shuls but in all Shuls.