Riven definitely needs a buff now
With the new juggernaut game play, three top laners have been buffed tremendously. Three of them, she already has trouble with. I think it is safe to say that Riven needs a buff in order to stay in line in the top lane.
Garen is out the window when it comes to a debate versus Riven. Everybody knows he shreds any Riven. Now his base stats has increased, Riven will have a harder time up top.
I feel Mordekaiser will become very versatile and can pretty much play all five role. His Q and W will be very scary if he goes top lane. Mordekaiser is the least buffed out of the three, but in his current state, he goes evenly well with Riven already.
Darius, one of the three among the changes is the most terrifying for Riven. His base stats increased is insane. Along with that, Blood Rage will mean Riven have no chance in a trade versus Darius. His Q now heals him... does Renekton ring a bell?
Overall, all of them have their attack range increased. I think attack range and movement speed plays an important role up top. Riven's nerf to her movement speed was a big deal, countless times, enemy opponent have escaped from me with less than 100 hp because of that 5 missing movement speed. Now with these increased attack range, trading with her lane opponent will be tougher.
Nevertheless, I think Riven should be buffed.