There are a few reasons why we don’t want to instance gameplay effects. Gameplay effects in this system are intended to be data only. The only reason they are blueprints is for inheritance. The event graphs were never intended to be used and we have no plans to support event graphs running inside gameplay effects.
Instancing gameplay effects would have performance implications. One of the biggest considerations here is networking and replication. Replicating that many objects would be a bad idea.
If you need to use an event graph in this system you should do it at the ability level, not the effect level. Abilities can be instanced and support multiple options for how they are instanced.