Meh. PS5/XB2 will be easy enough to develop for after the PS4/XBO. Backwards compatibility for both will help also. Expect the transition to be a lot smoother than PS2 to PS3 and PS3 to PS4.
I'm also expecting a much smoother transition from PS4->PS5, than from PS3->PS4.
Thats one of the benefits of x86 and sticking with very simular designs in cpu+gpu, even the unified memory ect.
Not to mention there will be backwards coompatability, which will ease the transition periode at the start of the gen abit.
Necro-bump this 2020: http://gamrconnect.vgchartz.com/thread.php?id=229249
Bumb in 2021: http://gamrconnect.vgchartz.com/post.php?id=9047071