Some thought that Sony’s reveal of the PS4 Pro might be a reaction to Microsoft’s plans with Project Scorpio, but Masayasu Ito, who leads Sony Interactive Entertainmet Engineering Division, firmly denied that interpretation in an interview on 4Gamer.
Ito-san mentioned that the concept of a console with higher specs was devised early in the PS4 development. The PS4 Pro itself actually entered the active development phase in 2014. He also clarified that there was no reaction to the competition: the PS4 Pro is exactly what Sony originally planned.
On the other hand, Sony has noticed that in recent years some core gamers have become less willing to wait for the end of a console cycle to get a machine with better specs, and they have started to become interested in high-end PC gaming. Which is why Ito-san and his team started to consider whether they could offer something similar within the PlayStation family, and that was PlayStation Pro.