In message , Iain Archer
writes

Was it not once planned to go through Peckham Rye?

It still is - on the way to Clapham Junction.

When and why was that plan changed?

I don't think it has changed - although the Clapham Junction line is
Phase 2 of the scheme, not Phase 1, and dates for Phase 2 seem a bit
vague!

--
Paul Terry