It's exclusion if the choice is made for you, even if unintentionally.
No choice was made for them. If I build robot horses for people to buy and ride, but you dislike horses, I did not exclude you. You get to decide if you like the horse and make the choice not to get it.
I can choose, as a hypothetical example, to not read any threads tagged "5e 2024". My ability to freely make that choice is what makes it non-exclusionary, as it's a choice I can unmake at any future time I want.
Same with playing 4e for
@Micah Sweet. At any time he can unmake his choice and play it again.
If someone else decides that henceforth all new threads will and must be about (and tagged) "5e 2024", however, then anyone not interested in those threads has, in slow motion as the old existing threads die away, been excluded even if that was not the intent.
I can get the 4e books tomorrow and play it if I want, despite disliking the edition and it being out of print. Further, if I want to I can rip out all the classes and just shove in the 3e classes. It won't work very well, but I can do it. Why? Because no one is preventing me from doing it. There is no exclusion.
Further, when you apply the above analogy to D&D editions, we can see that prior editions(older threads) don't die away. People are still playing Basic, 1e, 2e, 3e, 4e, and 5e. Nobody has been forced to buy 5.5e just because WotC decided to make it and stop supporting 5e.
There is no difference that makes it exclusionary. To be exclusionary the person must be prevented from posting in those threads. If the older threads can still be posted in, folks are free to do so.
For 4e to be excluding
@Micah Sweet, he must be prevented from playing it. That he made the choice to play it and run it for a year and a half is proof that it did not exclude him. He then made the choice to stop, because he didn't like the edition. Next week he can make the choice to play it again. There is no meaning of exclusion that applies to him and 4e.