The fact that Game Freak has never created a quadruped Fire starter probably should've been a sign to people that they probably weren't going to stop the trend now. :x
Can I be honest here for a second? What exactly is so horrible about final evo Litten? Okay, I get the point: It's not on four legs. People would rather have a Raikou-esque looking Litten evo than something bipdel that probably doesn't make much sense. Being truthful, I'm also not the biggest fan of Litten's evo, but I'm also going to say that I most definitely don't think it's the worst one out there. It's certainly far better in design than Emboar, at the very least (although that bar is probably low enough that it probably doesn't matter).
I dunno; with everyone hyped about how gen 7 is supposedly "changing things up for the better" this time around, I can understand why some people thought maybe,
just maybe, they would take a different approach with how they design the Fire starter evolutions.
Altairis already hit the nail on the head with this: it's not that this design is absolutely bad (although, I think the swollen hands and the fire-crotch-belt don't do it any favors), but when compared to all the other Fire starter evolutions, it's just more of the same. And it's even moreso similar when compared with Emboar, who is literally another wrestling Fire starter. But instead of being a boar, it's a tiger this time.
They actually managed to make the middle evolution work, which to me is the worst part. It's got a bulky upper body and smacks things hard enough to be considered a punch but still stands on four legs. That's a tough idea to pull off and they managed it. But a design that incorporates some sort of fighting style while standing up? That's very standard, very overdone. Someone who was unaware of the leaks would probably see the middle stage and get excited at the opportunity for a quadruped final design, only to have that snatched from them at the very end.
This is why people were so impressed when Pokkén Tournament included Suicune in its playable roster--it's
not easy to make a quadruped design work in an area meant for "traditional" fighting. Even if Litten's evolution had turned out Fire/Fighting, if it had been on all fours, it would at least show the designers were willing to think outside the box enough to try to come up with a design that worked for the Typing/concept they were going for, but have it be different in execution. But Litten's evolution is not different in execution, it's only different in the animal they chose to work it into.
Because of that, even if it turns out to be Fire/Dark, I still won't care for it. At this point, it's not so much about the Typing (although too much of the same in that area also gets boring) as it is about the concepts that make up the final design. We've seen this final design before, but with different animals. That's why I don't like Litten's final evolution.