Toxtricity would be very cool and "could" justify two voices (tho I don't know if they will treat the two forms having two voices when it shows up in the anime so who really knows) However, I feel it wouldn't be on top of the Pokemon Companies picks. Sakurai has said that when looking for new pokemon he asks TPC who a good choice would be and they so far always offer him the flavor of the month pokemon they want to promote most. Lucario, Greninja and most recently Incineroar.
So far, I haven't seen TPC give Toxtricity the same kind of attention and promotion that those three have gotten. Lucario debuted in a movie before it's generation showed up and both Greninja and Incineroar made many notable appearances in their seasons of the anime.
Now this season of the anime is odd, because it has ash traveling through all the regions which means his team is composed of a mix of generations (tho at least three gen 1 with pikachu, Dragonite and Gengar) The anime has also traditionally been a little less than fair to electric types in the past. Since Pikachu is an electric type, that means there is no room for one on Ash's team. And usually the generations pikachu clone gets adopted by one of Ash's companions, taking away another possible spot for any non pika electric type.
So, Ash won't have a Toxtricity, there are no Galar Gym leaders who use it (even the poison trainer added in the DLC doesn't use it, but if she shows in the anime she still could) And if Ash's companion, Goh, get an electric type there is a strong chance of it being Morpeko (tho that's not set in stone)
And we know from Incineroar that fan popularity isn't enough, since far and away Decidueye was much more popular than Incineroar was (and would have been less redundant as there wasn't already a final grass starter in smash like there was with the fire starters) So if who TPC wants to push most is the most important factor, I don't think Toxtricity has much of a chance, as much as I would love it (it, Graploct or Dragapult all would have been very welcome by me)
However, I don't think a pokemon is inevitable. Certainly possible, but no where near a guarantee. This year they aren't pushing pokemon that hard it seems. They haven't dropped support, but it's much more low-key then it would usually be. They said the DLC would be done in place of the traditional third version, but they certainly aren't selling it as hard as they would a third version. I could be wrong, but Sword and Shield don't seem like where Nintendo feels they need to focus this year.