update TODO

Author: samuelgruetter

language-adaptors/rxjava-scala/TODO.md

@@ -4,8 +4,8 @@ TODOs for Scala Adapter
 
 This is a (probably incomplete) list of what still needs to be done in the Scala adaptor:
 
-*    integrating Scala Futures, should there be a common base interface for Futures and Observables?
-*    Add methods present in Scala collections library, but not in RxJava, e.g. aggregate à la Scala, collect, exists, tails, ...
+*    Integrating Scala Futures: Should there be a common base interface for Futures and Observables? And if all subscribers of an Observable wrapping a Future unsubscribe, the Future should be cancelled, but Futures do not support cancellation.
+*    Add methods present in Scala collections library, but not in RxJava, e.g. aggregate à la Scala, collect, tails, ...
 *    combineLatest with arities > 2
 *    Avoid text duplication in scaladoc using templates, add examples, distinction between use case signature and full signature
 *    other small TODOs