Wasn’t what’s now the Rainham GTR service originally meant to go to Catarham or somewhere else off the BML, but there ended up not being enough capacity at East Croydon, absent the rebuild of Windmill Bridge junction (which now isn’t happening AIUI)?
It was meant to go to Caterham, you’re right, one thing I don’t understand is why they never simply took over the stopping service via Sydenham rather than the Caterham service being a separate service
Just checked Abbey Wood to Rochester, out of curiosity. Currently 46 mins. In 1982 (available on Timetable World) just 34 mins, with limited stops at Dartford, Gravesend, Higham (alternate services) and Strood only. Inwards from Abbey Wood it was Woolwich and Lewisham only, so it was a rare-example of a true semi-fast service operated by suburban stock (EPBs). With the importance of Abbey Wood, Woolwich and Lewisham as interchange stations greater now than back then, one would think that there would be even more demand for such a limited stop service than there was in 1982!
Another thought on the old Woolwich line semi fasts, was that until about 1993/1994 many of these services extended out to Ramsgate in the peaks and Summer months, certainly until the early 1980s they regularly went to Ramsgate (which another portion used to divide at Strood and ran to Maidstone West until the mid 1970s I think)
These ended upon the advent of Networker trains arriving and were curtailed at Gillingham, aside from summer excursions.
In todays era, given that from inner SE London down to Gravesend and along the Thanet coastal towns, is booming with new homes and becoming popular with commuters, such a service would be handy in ferry commuters and leisure travellers alike through several conurbations, you could have commuter flows from say Thanet to Dartford or Faversham to Abbey Wood then Liz Line to Canary Wharf (fares might be cheaper than Highspeed fares too) or Medway to Lewisham (anyone whose been to Lewisham recently will have noticed all the new towers and the town itself is being regenerated)
This service in 2022 would pretty much act as a people mover between these towns.