That is my understanding from several 2A advocates following this closely as well. They indicate a buffer tube that would allow you to remount a brace is a no go. If the buffer tube is required for the correct operation of the firearms, i.e. direct impingement, then the buffer tube should be a slick tube. If the buffer tube is not required, i.e. a piston system or similar, then you aren't allowed to even have the buffer tube.
I have stated the same thing as you and I got attacked and told I didn't know what I was talking about. But yes the general censuses is that one needs to have a smooth buffer tube. Unfortunately the brace rule is not clear on this and contradicts itself on several occasions. As has been said by many - clear as mud.
My suggestion here is this.
If you want to keep an AR pistol without a brace, then I would ere on the side of caution and use a smooth buffer tube that is not longer than 6 1/2" as mentions by the ATF. In the end, that is a decision that each person needs to make on their own. At least until we get clarification on 4 or 6 position buffer tubes.