The dialogue here between Oro and Tobirama then to Tobirama and Hashirama implies a few things. Tobirama the aggressor of the two Senju Kage is known for his ruthlessness, but also as kage would seek an alternative for the sake of people.
Based on that dialogue I had a theory that since Hashirama says "it wasn't a proper jutsu" he obviously knew of its conception before death but more importantly why it was made.
I believe it was a similar decision to Madara's to carry out Mugen Tsukiyomi in order to create a world of peace. The angle from Tobirama's side would be to revive the lost members of their enemies and or personal loved ones to shield themselves from the loss (or fear of loss) to create a world of peace. However during research and development of the technique he and hashirama (maybe even madara) decided to stop pursuit due to human life exchange or whatever reason until Orochimaru/Kabuto's re-development of it.
I also believe Madara may have had a hand in creating the Jutsu, since he broke the seal, or at least knew more detail than he claimed Hashirama did. Another side theory is that Madara may have realized "loopholes" like Orochimaru using Zetsu for Edo Tensei