On the latest Wrestling Observer Radio, Bryan Alvarez and Dave Meltzer speculated that either Enzo or Cass could end up as the attacker.
As reported before, it was speculated that it was Cass attacking Enzo, which would eventually lead to a Cass heel turn. But as we saw on Raw last Monday Night, Cass was the one attacked this time, that means it is also possible that Enzo was faking the previous attacks on him and could be the one turning heel instead.
It is also possible that WWE is leaving this as an open-ended question and option. There is also an open possibility that apart from those two, the Revival or the Big Show could end up as the attacker.
Source: Wrestling Observer Radio