Goroutines and channels make it very straightforward to set up an ECS engine hence you can actually run a lot of the engine in parallel and not have to stick to the "game loop" structure. Build your systems similar to the actor model with a mailbox, have an event/messaging bus, and you basically have a very performant engine.

I've yet to run into issues with the GC. The only bit of tuning I had to do was be careful with interfaces in hot paths and batch all graphics calls.