When I play as Finland, I will give bases to Soviets on Finnic Islands to avoid from the winter war.
Caving in to Russian demands would've handed over half of the Mannerheim-line, a land and naval base in southern Finland only 100+ km from Helsinki and Turku, use of railways from Leningrad to Hanko and total control of the Gulf of Finland. Finland would've been screwed and open to occupation, just like the Baltic states.
Also I am thinking of an event for annexation Estonia peacefully so that I can form FinEst Republic. Actually This would be an amazing national focus for Finland: Finnic Union with Estonia. Kinda Czechoslovakia.
Actually after Estonia had pretty much screwed herself over by caving in to Russian demands, Estonian president Konstantin Päts tried on 30.7.1940 to save the country by offering Finland a federal union with Estonia. At this point Estonia was a lost cause and Finland was forced to decline. He was actually arrested by Russian authorities later on that very same day.
Once Estonia was liberated (or occupied, however one views it) by the Germans the idea sprung up again. In Helsinki on 29.11.1941 Estonian Admiral Johan Pitka proposed to Finland's president Ryti a union between Finland and Estonia, which was again declined. Foreign minister Witting cited the fact that Finland would be unable to defend Estonia, and that "Estonians and Finns are by nature and state of mind so different, that they could not grow into one [people]."
Point being, even though a union between the countries is a nice thought, it's not something that would have happened in this time frame.
EDIT: That being said though, a national focus tree based around the idea of Greater Finland would be nice, but first PDOX needs to focus on creating a historically accurate or at least plausible Finland.