Could be my own changing perspective, but what I think is interesting is how the signal it sends keeps changing. At first, emoji-heavy was actually kind of positive: maybe the project doesn't need a webpage, but you took some time and interest in your README.md. Then it was negative: having emoji's became a strong indicator that the whole README was going to be very low information density, more emotive than referential[1] (which is fine for bloggery but not for technical writing).
Now there's no signal, but you also can't say it's exactly neutral. Emojis in docs will alienate some readers, maybe due to association with commercial stuff and marketing where it's pretty normalized. But skipping emojis alienates other readers, who might be smart and serious, but nevertheless are the type that would prefer WATCHME.youtube instead of README.md. There's probably something about all this that's related to "costly signaling"[2].
[1] https://en.wikipedia.org/wiki/Jakobson%27s_functions_of_lang... [2] https://en.wikipedia.org/wiki/Costly_signaling_theory_in_evo...