[meheleventyone]

There's a few things really:

Inter-entity/system communication without a bunch of tooling to support it is always going to be a bit cludgy and hard to follow as it's by necessity dynamic at runtime. It is really useful though so writing tooling for it is a good idea.

Perf impact could be pretty big if your ECS uses archetypes and needs to do a lot of copying data around as components are added and removed. But in my experience these sort of events tend to be low frequency so probably not terrible. Always good to measure though!

Don't feel hide bound to stick within the confines of the ECS setup. It's a tool not a way of life! Straight forward message passing might be much cleaner and clearer or there might be a better data sharing strategy that can live outside the ECS itself. All frameworks provide fun puzzles of how to fit functionality into them when going round them is sometimes simpler and clearer!