Could it be done? Finally we have the answer! A full Super Mario Brothers game ported to the.....Atari 2600??? Yes! Great job by homebrewer Chris Spry.
Available to purchase for $30 from the Atari Age store
http://atariage.com/store/index.php?..._detail&p=1016
....and the rom is released as well.
http://atariage.com/forums/topic/215...ries-released/
Here's a thorough review and gameplay of it.