Student accommodation is very popular with developers at the moment because per sq metre it makes more money. Look at similar developments along the old Kent Road, and in Peckham.
affordable generally means 80% of market rates. a new four bedroom family home maybe £4000 a month - affordable version of that would be £3200 a month you would need an income of over 100 K to be eligible for that. The location is ideal. It’s otherwise unused land in a long strip. But let’s see if Southwark Council does its job on insisting on at least 35% social housing watch this space.