So its down to Russia, Sumer and Arabia. And still there is another Civ missing with a DIRECT science bonus yield something (yeah, bonus eureka and bonus generall district adjacency doesnt count for me

).
Arabia will have the madrasa and it will be properly a UB/UD for religion, but it still might have some bonus to science like the mission of spain. But I think that might be not the case.
Arabia will be probably a strong mid game civ. Their UU will be probably some cavalry unit in the medieval ages, ranged or not, cant tell...
So we have Sumer and Russia for a flat Science bonus. So the chance are still high, that the Russians get a UB in the campus, maybe a better research lab like in Civ 4? Would be the second quite late UB after Japan's Electronic Factory. I think, that Russia will be a late game focused civ, Peter might give it sth general, but their UU will be probably not before the Renaissance, maybe the fourth late game unit as a tank after special battleship, submarine and fighter plane.
Maybe Russia is straight forward and just get the Tsar-Bomb as UU!

Kill everything in a 6 tile radius ...
So, Sumer will probably a civ with big early game advantages which they might preserve over time plus some general uniques. The UU will definitly be an ancient or classical era unit and maybe they get UI boosting food or science?