Honestly, I think everybody had that fantasy at least once or twice, on both sides of the whip, but it unless you're independently wealthy and live and breathe BDSM all day long, it's possibly the most impractical idea ever. Something for day-dreamers or people who aren't too well adjusted when it comes to reality.
It makes for a great fantasy and it makes for a really cool role play, maybe even for a great BDSM vacation or weekend, but day in day out, I just can't see it...
Imagine you're a normal couple, chances are that you're both working, at work - unless you are self-employed - you have a boss who is in control and makes the rules, plus at work you want to concentrate on work and not your private kink. Trust me, I'm very kink friendly but if I would have to work with somebody who's kink would interfere with the work, I'd be everything else but pleased and point out that they should get their sexual thrills at home, the time they're paid to work, they owe their full time and effort to the person who pays.
For it to be real and total power exchange, one person has absolute control, it can be hot for a short time, but if you want it as 24/7 you would have to micromanage and that's just a hell lot of work.
Of course you can agree to your own version of TPE, for example where the sub has a certain amount of freedom and the dominant trusts him or her to make the right decisions, however real life has a way of interfering in that.
In case the submissive is married or in a relationship with somebody else, TPE can't work, it's conflicting commitments and it's seriously unfair to the spouse (unless the spouse is happy with it too), who's relationship would have some serious interference by the dominant.
When it comes down to it, we all have lives outside of D/s and I really wouldn't want to deal with anybody who doesn't have another life and everything is just BDSM, they don't tend to be the most well adjusted people, to be honest, they'd drive me crazy. Apart from the fact that somebody who would agree to TPE without limits is possibly somebody who doesn't value their safety and life at all, and the TOTAL in TPE basically means that there can't be limits or else it wouldn't be a total power exchange.
For me TPE is just another one of those buzz words, a fantasy far too many people take far too seriously, trust me BDSM and D/s can be very enjoyable with only a limited amount of power exchange and without dramatic labels, all it requires is to be an adult and responsible and not let your fantasy run away with you.
Like slavery, power exchange in BDSM is completely voluntary, so we are playing with a fantasy concept anyway, something no lawyer could push through, it's two or more adults agreeing to something because it's what they want and crave. To give up power and free will in certain circumstances with a trusted partner is absolutely cool, but I'm getting fed up with people using TPE as an excuse for bad choices or letting your libido overrule your common sense. Even if you have agreed to TPE, you haven't agreed to be a mindless robot, you're still responsible. BDSM is a game for adults, if you can't act like an adult, sorry, you really shouldn't be part of it! It goes back to "I'm your domme and not your mom!"