I prefer him as a sort of hidden Easter egg. Though I do see the appeal of acknowledging his accomplishments. I would prefer a separate tribute to him. Put "Randal 'the animal', terror of Old Russia in a strike or something as a secret boss, Xyor style or something. But I wouldn't want to lose the awesomeness of a secretly near-invincible vandal who murders unsuspecting noobs on their first patrols of the Cosmodrome.

Perhaps both, or people kill him enough, his reaches his final form for a day and stomps face.

I would be open to that idea, as long as the method for triggering him was not made public knowledge. New idea, courtesy of my girlfriend: add an achievement for killing him.