Well, just to address the rhetorical scenario, it may be a bit different for you to come out if it's at your wife's family's thanksgiving than it was for the uncle. Remember that the Uncle has been a part of all of their lives for as long as they can remember, so his coming out is likely to be more accepted than yours might be, because even though they've accepted you into their family, and you may really feel like part of the family, you're still a "new member." And your coming out will be filtered through the lens of you being married to your wife. Their first priority will still be their concern for her. I'm not saying they wouldn't be accepting, I'm just saying it's a bit bigger a hurdle than the uncle's.
But on the general topic at hand, I don't think I'd want to use Thanksgiving or any big event because we've had enough drama on events and I'd rather not contribute to it.
Plus, I don't want that turkey stealing my thunder.