This isn't a Nintendo thing, but more a Game Freak thing. Pokemon Sword/Shield is likely going to have a bunch of people boycotting. I don't really understand the logistics but I guess they had people upload all of their Pokemon onto some type of new Pokemon thing that is going to replace the Pokemon Box. (for a fee) Soon after, Game Freak announced that all Pokemon wouldn't be available in the new port. Lifelong players were furious. (I'm not one, just a very bored man at work on Reddit) The only way to show developers is by effecting their wallets.
It's actually a trifecta of fuckery.
The first and most infamous issue is Sword and Shield ignoring the National Dex in favor of strictly adhering to the current regional (Galar) Pokedex. Although (Ultra) Sun and (Ultra) Moon did the same, they still allow you to move any and all Pokemon over from as far back as Gen. III, with Pokes that weren't listed in the Alolan Dexes simply having no Dex entry to register.
The second issue is the presentation. The models were effectively future proofed beginning in Gen. VI, which wouldn't be an issue if they were adjusted accordingly to adapt to stronger hardware. This started becoming noticeable when folks pointed out how the majority of attack animations are still lacking in regard to Pokemon making physical contact with each other or just being more expressive period, especially compared to the ones in the Pokemon Stadium duology's successors (Colosseum, Gale of Darkness and Battle Revolution). And, of course, there's the infamous "N64 tree" that was pointed out in the Wild Area for shits and giggles at the notion of Game Freak being lazy.
The third and final issue is the new battle mechanic gimmick called Dynamax. Basically, fans are pissed at it because it'll apparently be the only battle-oriented gimmick in the games, whereas the Alola games have both Z-Moves and Gen. VI's Mega Evolution.
On a related note, fans also view it as lazy because of it essentially combining Mega Evolution's transformation aspect and Z-Moves' superpowered attack aspect while capping it off by turning the user into a gigantic version of themselves (which goes back to the model/animation issue), when remedial changes to a ton of Pokes could've been done via new Megas or at the very least via base stat changes, moveset alterations and/or Galar-based regional variants a la the Alola variants.
As a lifelong Pokemon fan, problems 1 and 2 don't bother me too much. Due to Gen. I capping at 151, I've always preferred completing the regional Pokedex instead of the national Pokedex because of how each non-Johto game took place in just one region instead of across the world. As for the presentation issue, I'm alright with the retained animations and actually like the livelier NPCs, although stuff like the "N64 tree" is inexcusable when it's on the same system as BotW.
When it comes to issue 3, I'm pissed because of the sheer laziness behind it. Game Freak said the removal of Megas was done for balancing issues, which is nevertheless a weak-ass excuse when they could've simply altered stat spreads and/or abilities for Megas accordingly. Z-Moves not only allowed any
Poke to use a potential nuke-tier attack, but also allowed for wild card strategies, so removing that was an even bigger fuck up on GF's part, in my opinion.
In the end, I still plan to get Shield while my sister nabs Sword. At this rate, however, I wouldn't be surprised if they wind up being on par with X and Y as the mid-tier Pokemon games in my personal tier list: Pretty good, but could've been so, so much more.