Old Kent Road has a new housing number cap in place that can only be lifted if the Bakerloo Line Extension is approved. Lewisham however could do with this extension with the level of housing now and the fact its housing target was recently uplifted by central government (quite where such housing will go though given the dense high rise blocks in the area now).
This is a timely reminder though of how much Southeastern have benefitted from offloading routes onto other operators while retaining rolling stock: throughout their history they gave Redhill-Tonbridge to Southern, but most notably Blackfriars-Sevenoaks and London Bridge-Gillingham/Rainham to Thameslink. Despite this, they still struggle to have stock for widespread 12-car operation (granted platforms/sidings in places also influence this). While we're talking 2 decades at least, if the Bakerloo line to Hayes happens, that's a huge capacity boon for Southeastern, both in terms of stock made available for use elsewhere and paths into London Bridge and Charing X, which would affect the next metro fleet.