Almost no addons communicate in channels blizzard is restricting. as others said, like 99% of addons are fine with party, raid, guild, whisper.
The real concern is addon authors for the addons they are intenting to break with this are ALREADY talking about just buildinga mesh network over whisper syncs, which means blizzard will get mad and break that next, and that will break a few addons then. The authors in question don’t care about the spirit of game and would rather watch blizzard gut eve…
It really isn’t something that’s going to break anything as we just have more sophisticated modders now who can create more interesting solutions and work-arounds.