The way that video is going viral

it's gaining 1M views every hour now

this rivalry is so iconic and clearly still fresh in the mind of the general public, both Britney and Christina have hit a slump in their careers and I personally think it'd benefit both to capitalize from it by dueting or releasing some sort of viral material together.
It would be messy as hell online, I mean, look at what this did to Exhale? it basically became a Christina forum since yesterday

but it would raise their social media and overall public presence tremendously. It'd benefit all their upcoming proffesional ventures, be it Britney's Vegas gig, her lingerie, or Christina's music, the Voice, her perfumes, her stint on Nashville, her new TV show for ABC Family, her upcoming 4D Brodway debut, her Peter Pan OST track, etc.