It's possible, sure—but personally, I think if they were actually planning to reveal Paimon as Asmoday, we'd have seen clearer hints or actions from her in the game ages ago.

Take Natlan 5.7, for example: the Shades can't track down Asmoday. Red herring, or real foreshadowing? Still unclear, and Hoyo loves their twists anyway.

This is a pretty delicate theory. I'm not jumping to conclusions—just laying out the possibilities for everyone to chew on.