He was eager to talk to Taka'aki—after that conversation, Taka'aki thought of Rum's signature phrase. If Hyōe is just Rei's/Tōru's NPA boss, then he may be looking to loop in the older Morofushi on the plan Team Conan's proposed to Rei/Tōru (the plan that still hasn't been revealed—just like the plan they came up with during the Vermouth arc climax).
Apart from that, he did go out of his way to approach Rumi—Rumi's probably related to any purely personal motives he may have—yet he didn't intervene while the Kyōto case aftermath was going down, like Kanenori (and to a lesser extent, Rumi) did. He even ordered Rei/Tōru to help Shinichi/Conan out with a case.
Out of the 3 suspects and Muga, I'd be most surprised if Hyōe turned out to be Rum, honestly.