Ask any group of Magic players who were around for Future Sight what the best and the worst parts of the set were, and chances are you'll hear Steamflogger Boss come up many, many times in both categories. One of the most infamous cards in all of Magic, the lord for a tribe that never was (save for one hilarious Moriok Rigger update) featuring a keyword that may never be (oh, to think of the countless threads on MTGSalvation's Custom Card Creation section featuring possible designs for assembling Contraptions), it's widely considered a kind of Un-card in a serious set, an elaborate Dadaist joke. Future Sight was known to contain some red herrings, and none was more obvious than this one - or is it?
It all began with one seemingly innocent question to Mark Rosewater on his Tumblr blog, when hawkps asked, "So, what's the deal with steamflogger boss?" Despite getting a typically Rosewaterian joke answer - "He’s not the nicest of bosses. Always flogging with the steam." - the question seemingly sparked a discussion that points to hope for redemption for the Boss and his Riggers in the Izzet League of Ravnica.
When cervantes3 asked Mark, "Do you think next time we go to Ravnica the Izzet could have an artifact related mechanic, or are they too entrenched in an Instants and Sorceries matter mindset for that to work?" he responded:
The problem is that Ravnican sets with all the multicolor guild responsibilities doesn’t have much room left for artifacts and you need a certain threshold to have an artifact subtheme.
Since Contraptions are, seemingly, necessarily an artifact subtype, this would initially rule out a Ravnica 3 version of the Izzet getting the long-rumored mechanic, but then, Mark agreed with habba84's assessment that the Izzet need a more mad-scientist-like keyword, and colored artifacts do exist and would not force a multicolor set to have extra artifact slots (this was done in Shards of Alara block, of course).
It was keated who finally addressed the eight-hundred-pound gorilla in the room, saying "Was there ever a thought to make the Izzet mechanic 'contraptions'? Seems like it'd fit them just fine :)" Mark's response was cryptically specific:
Ravnican blocks with ten guilds and ten guild keywords do not have space for excessively complex mechanics.
This seems to indicate one of two things - either an assemble-Contraption keyword has already been floated through R&D either as a thought experiment or for actual future use, and it is extremely complex; or R&D is trying to find a way to simplify the Contraption mechanic as a way to have a flavorful mad-scientist's-creation keyword. Complicating the issue further by seemingly coming out in full support of an Izzet artifact mechanic, Rosewater told fetus-pizzas "the Izzet love [artifacts]" despite red's destructively-inventive side and said to doopboopdoop that "Izzet is flavorwise the correct guild to love artifacts."
All in all, the final fate of the strange Rigger and Contraption subtypes lies in the hands of public opinion - when su92 asked, "If you somehow managed to make contraptions, how much of R&D would be happy?" Rosewater replied:
If enough players are happy, R&D is happy.
Contraptions have their supporters even when no one knows what they do; and a well-executed version of them could win others over. Does this mean they're likely to appear soon? Not by any means - the "Izzet need a good, appropriate artifact-related mechanic" talk puts their earliest release at Ravnica 3 block, which is, optimistically, at least five years away. But five years isn't forever.