I wasn't saying you're wrong, just that the odd name gen getting leap frogged is more coincidence and fans trying to see patterns that aren't really there more than anything else.
Smash right now is slated for this year, and we know nothing about Gen 8 yet. We don't even know if we're getting the games at all this year. But of course behind the scenes is a whole different shebang.
But even so... Sakurai has the final word. If he wants someone from Gen 7, he'll put him in the game. Simple as that.
Pokémon's in a rather peculiar position at this point.
On the one hand, Gen 7 is currently ongoing and was likely in development alongside Smash, they have established Pokémon that people love, it will probably last a decent while longer even if it's on its dying breath, and it is Pokémon's 20th anniversary games. So theoretically, there is good reason to believe that they'd pick a Gen 7 Pokémon during Smash's development since the Pokémon are there and Sakurai would have good material to draw off of.
But then there's the weirdness of Gen 8. It's been announced, it also was being made during Smash's development and may've been in conceptual development even before SM came out (we know XY began development around BW's release for instance), it's slated for this year and based on the financial report in January, they're still gunning for that date. Also, they'll likely probably start promoting it at least after the Summer since localization is rumored to be underway, we're implied to get new Pokémon for the movie, and Pokémon's general media is looking to run out of USUM merchandise material come this Fall. So with all of that in mind, Gen 8 is looking to be where the focus will shift during the Fall, and whether it hits its 2018 date or slips into 2019 (though note, I doubt it'd release anywhere past the Summer in that scenario) theoretically they could've talked to Sakurai and together they pulled another Corrin/Greninja type deal for it.
It just depends on how much information Sakurai is privy to, how much the Pokémon in either generation appeal to him, and whatever's going on behind the scenes with Gen 8. Personally I'm honestly on the fence since Smash 4 did crush the dreams of many Gen 5 Pokémon by skipping over them for Greninja and history can repeat itself, but I also acknowledge that it's not the exact same scenario either since Gen 8 won't be out (or will have just come out) when the next Smash game likely does and that could shift things in Gen 7's favor.