I'm curious when the 2016 tour dates will be released.
Get in touch with the Rick Steves tour office in Edmonds and ask them.
Usually the tour dates are released in late August/Early September. They often appear here on the website before receiving the brochure in the mail.
Here is the thread from last year and it looks like they were first spotted in June. I thought they were released in batches and the answer from Casey confirms that.
Off-Season or "winter" 2016 departure dates are expected to go on sale in mid-May, with the bulk of the schedule coming out toward the end of August, as has been typical in recent years.