My teen, no status, received glossy book in mail for first year free for MileagePlus Card. Says - invitation-only offer, $0 Annual Fee for first year, then $450. To be eligible, you must be original recipient of this mailing and apply at the URL above using existing MP number. MPCLUBCARD.com/rsvp17 by March 15, 2017. (United Club membership and No Close-in Award Travel Booking Fees seem to be best perks).
I already have a (paid) MPC card, but clicking the link above and signing in showed me be eligible for the "first year free" offer. I didn't pursue it, because I don't see it actually "working"... i.e. it's obviously a "promotion" and I already have it, so what do they have to gain by comping me?