The most divisive aspect of Scars of Mirrodin block, and the most divisive mechanic in recent Magic, tied perhaps with transform/double-faced cards, has to be infect. Some players loved the Phyrexians' flagship keyword for its sense of brutal inevitability, the necessity to build around it and the many interactions with previously innocuous cards it enabled, and the sheer fact that it was a nostalgic alternate win condition. Others hated it because of its mechanical parasitism, the fact that poison counters couldn't be removed, and the degenerate combos it enabled.
Since Phyrexia is almost guaranteed to come back as the villains of a block in the near future, foxtrot929 asked Mark Rosewater on his Tumblr blog, "All this infect talk has made me wonder, could we see Phyrexians return without infect or poison counters?" He put the question up for discussion:
I don’t believe the Phyrexians have to have infect or poison although the ones from New Phyrexia are pretty connected to it.
Let’s turn this to you guys. When next we see the Phyrexians, do you expect there to be infect?
The responses were, in fact, overwhelmingly "yes": johnnycoffee wrote "Infect seems pretty iconic with Phyrexians. IMO the next coming of them should have infect, but have it alongside newer concepts, which should probably take the spotlight," while sonsofsauron said "I think tying a brutal, inevitable mechanic like infect to the new phyrexians is awesome. I’d totally expect some take on infect when we see them again."
Given this kind of player response, and the fact that it has indeed been since Scars of Mirrodin block that -1/-1 counters were used, when the Phyrexians return it may be due time to reuse infect. However, there are definitely other ways to show Phyrexia's infiltrating, viral nature - including poison without infect, perhaps enabling an Orzhov extort-style stall-and-drain game like existed in Return to Ravnica.
What do you think about infect and its chances to be reused? Let me know in the comments.