Unless you're advertising an upcoming release to generate interest in order to increase sales, providing release dates is a bad idea. Most of the time, release dates are missed. When that happens, people get upset. When the date is missed by a long time, people get very upset. It won't decrease posts, but will instead increase them as people complain. Even if you say "it should be out around this date, but may not be," you'll still have the same people complaining.
As for upcoming changes, the only changes that should be mentioned ahead of time imo are bug fixes. And Khaled often does mention those if there was mention of the bug(s) in the forum. If there's no mention of the bug, there's no reason to say it's being fixed. And new features can be pushed back even at the last minute, so including them just gets people hoping for something only to be told they have to wait 6 months more to get it. In the end, it just causes more problems. Besides, it doesn't matter if you post that a bug is going to be fixed in a upcoming updates file. People don't read the current stickies. Do you think they'll read that before posting about it?
It's much better to just state right out that release dates and changes are not going to be given prior to release. You get the occasional posts asking for them, but they are few and far between.
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