Every other app on my computer can display emoji properly, except LibreOffice, so I assume Electron is just a bit crap

Could you explain this a bit further? I think as long as you have the fonts installed then Electron should show them correctly. Alternatively, there are emojis like :heart:, but currently I think the clients are rendering those with images rather than your system's emoji typeface. We could disable this, but I think it would cause problems for people without an emoji font installed. Maybe it should be an option in the settings?