It's actually incredibly popular. It's pretty much the default processing technique for bass at this point. I'm not going to spend an hour finding you dozens of videos with world class engineers (Warren Huart, Joey Sturgis, Eric Valentine, etc.) who demonstrate how they do it, but you can look it up for yourself. It's not a fad or outdated technique. It's pretty much the only way metal bass is ever processed -- in fact, there are literally plugins like Parallax that do exactly what I'm describing -- but it's also very common in rock and punk. And some bass distortion pedals effectively do the same thing using their crossover control. And it certainly doesn't come from multiband compression. Splitting bass signals has been going on since the '60s. You can read about Geoff Emerick using a bass DI and an amp for Paul McCartney in his book Here, There, and Everywhere. Phase coherency was ensured by ear.
And I'm not sure what I'm "not understanding" about a high pass filter. Care to elaborate? HPFs don't apply differently to bass amps than they do to anything else. Everything is about signal chain. If you run the hpf before your saturation, you're feeding the saturation less low end. I'm not sure how that's up for debate. A HPF is a HPF. The only thing that change are the slope, how high you set it, and where you put it in the chain.
I assume you're grandfathered in here based on your meaningless vague comment getting several likes, but I'm interested to see if you can back it up with any substance.