So i found this video about Riven and Fiora right now.

https://www.youtube.com/watch?v=aa3PFnX-KLM

TLDR: If you don't feel like watching, basically Riven should be a good pick into Hyper Carry top laner's, or laner's that lack a good/safe laning phase. Tanks are usually pretty safe lane phase so they should naturally counter her, but they don't because they've been nerfed pretty bad.

In addition, her item's have all been buffed, 40 AD on GA is pretty huge for her, death's dance buff has cause a HUGE amount of problems overall since it was buffed and this is the main reason she's really strong right now. Fiora's should be punished for having a poor lane phase, but at the moment that won't happen, she's very strong in lane and scales EXTREMELY hard into late, again due to the itemization changes.

I'm with Exil on this, i don't think the champions need nerfs at all, they were fine before the recent changes to their items, so reverting the items or nerfing them is a probably a step in the right direction when it comes to putting them both back into a balanced state.