Apparently there was a Super Mario game called Super Mario Special that was released for PCs in Japan. It has some new items and power ups.
You Ann also see new skins for SMBC which include, SMB2 (8 and 16-bit), SMB Special, Atari, and Castlevania.
You can also see other playable characters in the trailer.
These guys are doing such great work for a game they aren't making money on. They could have stopped with version 1.0 and it still would have been great, but he we are, 3 years alters, and a game that is building better ideas onto the original.