The Beckenham Junction to 'Bromley' (very vague destination) idea came out of the Bakerloo Line extension proposals, the idea being it would takeover the heavy rail Mid Kent line to Hayes, with every other train diverted after New Beckenham via the spur to BJ. I believe my old employers the London Borough of Bromley paid out for some so-called consultants to present a glossy folder showing how it could miraculously get beyond the Junction by wish fulfillment alone: suffice to say no civil engineers, or even uncivil ones, were prepared to admit they played a part in this presentation.
I'm pretty sure I read somewhere that the extra loop proposal had been scrapped. Croydon Tramlink long ago lost its prime instigator on the operational side (Peter Hendy) and a Mayor who, despite his numerous faults, was very pro-tram (Ken Livingstone.)
By the way, I never saw TfL publish any plans, even as kite-flying, to extend along the main road via Mayday Hospital to Thornton Heath Pond: it sounds like a
Croydon Advertiser story to me, or the attempted election bribe of a marginal seat MP.