I agree that positionless could lead to some weird outcomes. It's possible that a future team could have five guards, for instance. But, ultimately it's about rewarding the best players (especially where there are contract incentives involves), so I'm fine with the change.
'94 and '95 are what comes to mind for me.
Shaq, Hakeem, David Robinson, and Ewing all finished Top 5 in MVP voting both years, so likely all would have made 1st Team if voting was positionless. Ewing got the short end of the stick and didn't make an All-NBA team either year.
Also not unfathomable to think of a season semi-recently when we could have had 4/5 of Westbrook, Curry, Harden, Lillard, Paul, Rose (if never injured) make 1st team, if things lined up a little differently from '15-'20 (and Kawhi/LeBron/Giannis are injured, taking a baseball sabbatical, undiscovered in Greece, etc.).
I'm kind of torn on this. As others have just mentioned (Roy, slam, Celtics2021, etc.), NBA is mostly positionless, and except for some PGs and Cs, most players don't spend all their time in a single position. But if you're a Center like Ewing in '94 should you make the team when there's 3 players better than you at your position? Are All-NBA contract incentives supposed to reward you for being the top 3/6 at your general position, or top 5/10/15 in the NBA? Is All-NBA intended to be more of a best players at your position ranker, or best player overall ranker (and if best player overall ranker, how is it that different than MVP)?
And then there's All-D. Probably more likely to regularly produce teams of 5 forwards/centers. But if you're one of the best at defending opposing guards, even if there's 10 forward/centers ahead of you, I think you should be recognized.
I think All-NBA/All-D should somewhat resemble a team you would actually put on the floor if given a chance. I'm okay with one of Jokic/Embiid not making 1st team because there's a better player ahead of one of them. I'm not okay with Jaylen Brown not making a team because he's split between 2 positions. I don't know what the best solve is though. I'm just not convinced positionless is it.