it makes me think about how both reactions and zaps could be integrated into replies, and then to link the two parts together to prioritise them or highlight them

would just entail probably adding a multi-letter tag like "associated" and the reply ID with the zap/reaction on the input side and pulling that out of the set of events that refer to the parent note, and then parsing that for display so reactions get attributed more visibly... and for fun, add a priority feed that puts zaps at top and reaction comments below it