Contrariwise to your blatant assumption, I'm not proposing a system where users can edit each others' posts. I'm just toying with the idea of word filters, not too different from the ones that already exist for slurs in Lemmy.
For example. If you write [insert slur here], it gets replaced with removed. What if it replaced emojis with "I'm braindead."? That's it.
(Before yet another assumer starts doing its shit: the idea is not too serious.)
They would be less obnoxious if used sparingly, but they wouldn't be effective unless the reason why they're used changed, from graphical echo ("I saw a cat today 🐱") and mood/attitude particles (like you did) to ideographic usage (e.g. "I saw a 🐱 today"). Plus they're still colourful and attention-grabbing drawings within text, they detract attention from the text itself.
They can but most of the time they aren't. That's the key here: most of the time emojis only add noise, to the point that the shreds of legitimate usage (that can be conveyed through other means) don't really justify keeping the cons of the noise.
It isn't like anyone would implement my idea though. I'm mostly doing like that old man screaming at the sky, or something like this.
What is the point that you're trying to convey by relexing "old man screaming at the sky" to use emojis?
If the point is that "they could be used to convey meaning": I've already addressed it. Usually, they aren't. (If the point is something else, please clarify.)
However my point is not against the usage of emojis to convey linguistic meaning, like that. (It's a bit pointless, but at least you're saying something through the emojis.)