I fear that theres a deeper reason to the mobile authenticator... Steam phone?
You want me to let you in on the big secret? Okay, here I go...
IT'S FOR SECURITY YOU CUNT.Here's the dealio. Activision-Blizzard and Square Enix have been using mobile authenticators (not phones, but physical dongle things you had to purchase) for a long time, and they've seen massive success in decreasing the amount of scams. Valve are obviously wanting to try and increase the security reputation and also reduce the amount of Steam Support account-related requests, and so they're trying to find convenient and cheap ways to help (stupid) users with this scammer issue.
I don't see you suggesting anything better that would actually work, so maybe just shut the forget up.
You won't be able to sell cards that expire like summer or winter cards because they will expire before you get them over to the market.
And yet I feel like Valve probably already have an internal solution for this problem.