(First post, so please bare with me....)

Blue1 uses SAS EuroBonus as their FFP so the same rules apply than on SAS. Remember that Blue1 does not have a Y+ product (Economy Flex with SAS), but offers full service in Y on all routes.

My experience is that in case of overbooking Y class both SK and KF give automatic complimentary upgrades to travellers in this order:
1. EBP + travel companions (regardless of status)
2. EBG + travel companions (regardless of status)
3. *G
4. EBS

Additionally one might get a complimentary upgrade from Y all the way to C by requesting it at the gate provided that:
a) there is space in the front cabin
b) the person handling your feels you deserve it (depending on his/her mood and your status/tidyness)

Paid upgrades:
My experience is that at least SK honours status more than paid upgrades. I for instance (EBG) have been automatically upgraded with my travelling companion from Economy to Economy Extra (even though travelling on a Q fare). And then after boarding reseated from E-Extra to Business because somebody else bought an upgrade from Economy to E-Extra. This happened even though my tavelling companion didn't have any status at all on SK.