I fear it would make the current issues worse. Sure there could be people who genuinely want to learn and get better, but the reality would be that people would put that icon on as a justification to play bad and not learn.
I think if you're actually trying to improve, saying it in chat, even if its through macro, is the best option.

I would also say that the pace of the mechanics that is in current dungeons or trials can be mitigated by just sacrificing your damage output. Leave optimising to the sweats.
With tanking mobs you can basicly make a plan to follow, what mitigations you use at which moment, since most modern dungeons follow the same pattern: 2 trash packs -> wall -> 2 trash packs -> boss. You usually dont need defensives for boss, maybe the short cooldown like the blackest night, which is not an issue.