I personally think they're (SAS) entering an over saturated market here in London. That is to assume they'll be going after the Leisure traffic.
LGW would see them off with fierce competition from not just Norwegian, but EZY are massive at LGW and BA will defend their turf here also.
STN has Jet2 arriving next month with a massive fanfare, Ryanair, Easyjet and now even BA in the shape of Cityflyer all have a presence here big and small.
Only airport left is Luton, but I think over-night stands here are a problem, plus EZY would put up a decent fight. Not sure there's much fight to be had from Monarch mind?
Southend anyone?
I just can't see it lasting, it will just be another Aer Lingus IMHO.