Will I have access to any lounge at Keflavik airport?
Was in KEF today Nov 6 2017. SAS Plus (or any SAS) does not have access to Saga Lounge in KEF.
The SAS Plus page you linked, does mention the access to lounges. However it does also note that this access is subject to availability.
The only lounge at Keflavik seems to be the Saga Lounge by Iceland Air. In its access rules, Iceland Air mentions Eurobonus Pandion when flying with SAS, and SAS Passengers on Business Class (C-class), but not SAS Plus passengers (adapted from here):
It seems that SAS Plus is in fact equivalent to SAS C-Class. Hence SAS Plus passengers should have access to the Saga Lounge at Keflavik.