I don’t think this is (yet) available with ENV. You could suggest it, but note 1.9 is in DEV, not out so this feature might go away (I doubt it though). I think it shouldn’t be needed, if the GC was actually better, more aggressive be default.
I don’t know if other languages have a similar option (then most likely Java, not Go I think). You could make a PR for an ENV, but while I think the option (as is) is is useful, at least as a debug option, I don’t think we’ll need this in the future, which is coming fast. There’s a lot going on with GC, many PRs already and some merged. People are doing good work on it.