When I was originally trying to implement this code, I was trying to implement it as an event gateway on ACF. While that worked fine on ACF, as you initially pointed out, event gateways in Lucee are quite a cut and dried as they are on ACF. Also, a buddy had asked me why I decided to go with an event gateway when it could have been refactored to a cfthread. The event gateway code was introduced way before cfthread was an option, so respecting his opinion, I decided to go that route.
As far as impact of running the thread on busy application servers, I haven't run this implementation on any server with any amount of load. Mostly this was a PoC application just to see if I could implement it; I am afraid I don't have any hard data on how it would behave in a production environment.