I can't even imagine how dysfunctional the management of your development teams must be if you can't even forecast releases a few weeks away with reasonably certainty.
We have done recently - Desperate Measures was announced 3 weeks in advance - but each piece of content differs in development. Some fly through, others unfurl surprises to tackle.
Just speaking personally, in other development teams I've worked in, content is usually announced pretty close to release for similar reasons.