Oh okay, I was just wondering given that its the only other region with a Swedish speaking majority.
Only the coastal part of the province has a Swedish-speaking majority while in the inland part Finnish-speakers are more numerous. AFAIK there were some separatists also in that area, but never as much or so vocal as in Åland.
One important thing is that the Swedish People's Party, SFP, was against separatism in both Åland and Ostrobothnia. Why? Because the minority is scattered in different (coastal) parts of Finland and the party had to look after the rights of their constituents within a Finnish state. If Åland breaks away, and if even a part of Ostrobothnia follows, the rest of the Swedish-speakers in Finland would lose their voting base and most of the considerable political clout they had in Helsinki.
Åland managed to get very confortable terms from the Parliament in Helsinki as an autonomous province even
before the LoN ruling. After the ruling, the autonomy was even stronger. As a part of Sweden, the islanders wouldn't have half the semi-independence they have had for almost a century now.
It is possible, now, that also the coastal part of Ostrobothnia could have broken away as an autonomous province/enclave and secured almost similar rights had they pushed hard enough. But pushing too hard might have also backfired in a way that could have seen the Swedish-speaking community marginalized, harassed and pushed to these two enclaves as the Finnish-speaking majority would have been more negative towards the minority because of their "special rights".
Both the pan-Swedish fringe on one side and the most ardent Finnish nationalists on the other favoured separating the language groups to linguistically as "pure" areas as possible. The moderate majority on both sides opposed this, advocating a bilingual state. While it might not be in every way the most ideal solution, at least the policy has kept language strife to a minimum in Finland since the early years of independence.