>In that case how tricky is the federation work on the backend? As for the frontend, IMO just copying Pleroma's UI design for emoji reacts (emoji react button that leads to picker with search + emoji reacts shown just above buttons) but I don't know how painful that is to implement.
Sure, I'll probably make something similar to Misskey and Pleroma. But it's a non trivial task, can't tell how much time it will take.