I wonder if this is too featureful? What is the difference between +1, heart, and hooray? Having just a +1 and -1 is unambiguous and probably covers the vast amount of use cases? Perhaps not, but I'd be very interested to know the reasoning between being choosing between "unambiguous" and expressive.
Internally at GitHub over the past few weeks I have been using the heart reaction to express appreciation. For example, if someone is very helpful or empathetic I let them know I appreciate it with a heart.
People have been using emoji comments to express not only reactions but also for voting. Even if you were to add voting features (which reaction emojis can be used for) you'd probably still get unbearable amounts of zero-value comments comprising of a single emoji, "+1" or gifs.
This is probably an attempt to break that "user habit" by providing a tempting alternative to the type of person who spams comments in issues.
Additionally, by using emojis for voting maintainers get slightly richer data about how users feel about something. A user story with 1000 thumbsups might fall lower in the backlog than a user story with 1000 hearts.
