Would you be here for a Bey x Justin album ala Tammi Terrell x Marvin Gaye
Tammi Terrell and Marvin Gaye were the premier Motown vocal duo and released a bunch of classic albums and songs together. Most notably "Ain't No Mountain High Enough" and "Ain't Nothing Like the Real Thing".
The latter was covered by Beyoncé and Justin at Fashion Rock in 2008.
the chemistry...
The reason why I think it'd be a good match is because they're both contemporary R&B musicians who've focused on fusing the modern with the old. I think they'd be able to create a cohesive and inspired record.
Why waste your musicality on a hip hop record (it's one of my fave genres, but for a singer, they run the risk of being relegated to a hook) when you have a friend that's your equal in skill and who's voice would compliment yours. If Bey is gonna do a joint album, let it be with someone who'll push her musically.