We did consider (and regret) potentially leaving android behind, but we were (perhaps naively) hoping that something like retrolambda would suffice, or that android would catch up. In any case, it doesn't make a lot of sense to have 2.12 still support Java 6, since most of its features require Java 8 (those that don't, we first implemented in 2.11.x).
As announced in http://scala-lang.org/news/2.12-roadmap/, we will continue to support 2.11 for a bit longer than most releases, and we welcome community backports of 2.12 features that you'd like to see in 2.11.