I agree. ...which is why I made sure to write, 'equal member'.
I think Texas would also get a pass on the unwritten (although it may be on paper somewhere) rules of expansion for both the Big 10 and the SEC.
One thing is certain in all of this, is that rules can be broken. But in this case you have to ask yourself what would it take to break the rules and that can sometimes point you in the direction where you find the truth.
Would the Big Ten break with their traditions to invite Texas? If they thought Texas was in play and the SEC was going to snap them up if the Big Ten did not and the Big Ten thought they had more appeal to Texas than the SEC, perhaps they might break the rule.
But which conference would appeal more to Texas? The culture is decidedly in favor of the SEC. The style of play is decidedly in favor of the SEC and the geography is also in the favor of the SEC. So of the three biggest reason to go - besides money which is a moot point. The SEC wins all three - imo.
The Notre Dame thing with Texas? Texas does not love Notre Dame, Texas has and has had some people connected to their university that loves Notre Dame. That is the distinction that matters.
The appeal of the Big Ten to Texas has to be limited at best.
But can Texas go to the SEC? Had Texas left when Texas A&M did, Longhorns could state they took their version of Marshall with them because they had too, even if it wasn't true. Appearances matter. But several years after Texas A&M has left, Texas would basically be admitting that Texas A&M was right and they had to follow THEM!. Appearances matter!
I have stated it many times. Texans are smart about money and business except when it comes to their pride. There isn't enough money in the world to buy their pride and there is no business they want more than running that pride.
So to answer your question, could the Big Ten and/or the SEC make the exception? Sure, but they would not. Neither needs too and neither has anything to gain from adding Texas. Texas, because she is an 800 pound prima donna, is not unique to either conference. The only thing Texas could be purported to bring would tv markets but the SEC already has that covered and the Big Ten could fix that too with a lot less headache than having Texas and all of the drama baggage she drags behind her.