I'm running G1 on my - large heap & many CPU cores - production systems for quite some time. Did this after benchmarking on ES 6.0. G1 was significantly faster for my setup.
I'm also very interested in the status: no reply on my last question about this Reasons for not using G1 GC?. I cannot find a currently valid reason for not using G1. Especially interesting since G1 is the default CG for Java 9...