Who was Obito going to revive? I just watched the recent episode (391) and just prior to Obito being taken over by Black Zetsu, he seemed to have acknowledged his sins and was planning on using Rinne Rebirth - but for whom? It certainly wasn't for Madara because Black Zetsu wouldn't have gotten involved. Jiraya was on his mind, so was it him? Or was he planning on reviving all of the ninja who died during the war?
Obito was trying to revive all the people he killed in battle, the way same way as Nagato did.From here


  Obito attempts to amend his mistakes by using the Samsara of Heavenly
  Life Technique to revive those he killed, noting he had finally
  understand why Nagato betrayed him. 


For your question why Nagato didn't revive Jiraiya... My guess is the dead people will
 be revived from where their dead body is,


  Since Jiraiya's body was far too deep in ocean that even Kabuto can't reach to
  collect his DNA, it would be waste to revive him. Even after reviving
  he will die because of water pressure. So Nagato didn't try to revive
  Jiraiya.


It is also mentioned in Jiraiya's wikia page


  Later on, Kabuto revealed that he attempted to retrieve Jiraiya's body
  to bring him back through Summoning: Impure World Reincarnation, but
  it was far too deep in the ocean for him to reach without being
  crushed by the water pressure.