Palpatine killing Maul makes the most sense at this point. It has to be him or Vader imo. Maul's story has outgrown his feud with Obi-Wan. His nemesis is now the Sith. Vader replaced him, so that is a thing. Palpatine was his master.
I don't agree that Maul's story has outgrown his feud with Obi-wan. It is because of Obi-wan that Darth Maul was replaced by Vader and as Maul pointed out, he will want revenge on "all of his enemies". I'm not sure if that means Maul somehow knows that Obi-wan is still alive but if it does, then Maul will view Obi-wan as one of the top 3 nemeses. Maul would want to kill Obi-wan (for cutting him in half) as much as he wants to kill PalpSidious (for killing his mother and brother, using him as a weapon, and leaving him to die) and Vader (for replacing him).