Of course, you can show your generosity there.. I don’t think it’s against the forum rules. And even if it turns out that’s not the right section to launch it, the mods will probably just move it to where it belongs anyway. Just go ahead and start it; I’m sure I’ll be one of the many joining the prediction contest.
as long as it does not fall here.
To be specific, I'm referring to "Post in this thread for free x". That belongs in Games and Rounds. Though it isn't limited to that, in general you shouldn't be giving people incentives to post in your thread, it's disruptive to actual discussion.