Result of my painful self experiment: SK does a reseating in the DCS (similar to airport cash upgrades) and doesn't touch the original booking class of the ticket. So I got the usual amount of status miles with M&M for the original booking class (Q) but a seat in Plus. I made the mistake of checking in with LH for MUC-ARN-LLA before the bid cleared, so it wouldn't generate a boarding pass citing a cryptic message (due to a special service request associated with your booking you are requested to contact ground staff at the airport for assistance). The agent in MUC taking my luggage just mentioned 'you got reseated' and printed the boarding passes.

In the end it was a waste of 3000 points but they were expiring in June anyways