From MAN I can connect to the US via almost any European airline (or US airline come to think of it) and most give me lounge access on both sectors holding a J ticket for the long haul bit. Ditto with probably every other non-Scandinavian connecting passenger.
SAS must be mad doing this - the cost of lounge access for the first sector can't be huge compared to the £2k cost of a J ticket to the US.
I can still get access to the T1 MAN lounge with Diners or PP but that's chargeable.
I think this will backfire on them.