I've ever heard (don't know if it is true) that SN reservate almost 60% of the seats on the JFK flights of AA. So I think the second daily flight to EWR is absolutly needed for CO, because their flights will be too full if they simply upgrade to B772 I think.
The reason why they wait so long to announce, I don't know. Maybe because of the new AFI destinations, probably UA and CO are going to codeshare on some/all of these new destinations, and I think SN has not the intention to announce their AFI flights to soon (because Air France). But I think they will announce this, this week or in the first part of February.
Some nice things to be announced in the comming days/weeks:
-Austrian codeshare
-new AFI destinations
-US partnerships
-And for later in 2010 the replacement of the Avro's and maybe other new aircrafts to be announced (replacement B737, extra long haul...)