We need them.

Proposed api for generated methods:

Thrift:

service FooService {
  i32 bar(1: string arg)
}

corresponding Java:

public interface FooService {
  int bar(String arg);
  int bar(String arg, long timeout, TimeUnit unit);
}

Timeouts would be communicated via ServiceMethodCallback#onError(Throwable) - likely via a java.util.concurrent.TimeoutException.

The downside being, of course, that the number of service methods doubles. On the other hand, such methods are typically a small portion of the overall number of generated methods, so it may not be so impactful.