Our current thinking is that we will indeed require our Android users to enable Java 8 language-feature desugaring if they have not already. We expect that nearly all projects have done so already, since this is necessary to use lambdas, among other features.
(This affects only Android: For now, users of a Java 7 JRE
can continue to use Guava without taking any further action. But we will drop support for Java 7 JREs
in a release later this year.)