@viktorklang Because it results in a higher overhead for using JDK 8.  Mapper, for example, is not a SAM, and so cannot be used with Lambdas.  If we were to use Scala futures, the best we could have is wrapper methods, like this:

    future.map(Mapper.wrap(a -> foo));

Which is more verbose than what our current API offers, which is:

    future.map(a -> foo);