I think this trend has been around for a while now (it started to become more noticable for me at least a couple of years ago).

At first there seemed to be a correlation between how 'cool' the project was and the number of emoji, but now it seems like it's as expected as just having a README itself.

I've definitely seen _more_ decorated READMEs, and I can't help but feel like there's an inverse correlation between emoji count and readability.