Well, the silver lining from this is that his rap verse will possibly replace the awful callout section of
"This Is How We Do." Anything, literally anything, is better than Katy's callout section, even a Riff Raff verse.
And this isn't an E.T./LFN remix situation... Riff Raff isn't relevant at all and it's not on iTunes. She isn't trying. Riff Raff probably wanted to feature on it so she let him.