It would still require a substantial amount of work to do Continuation and Winter War-based maps for HoS. Custom skins for infantry, preferably some Finnish voice work, new tank skins, static meshes and map textures to reflect the terrain and vegetation of Finland accurately. All quite possible to implement, but would likely go much more easily if it were done as a compilation by a team of mappers and modders.
I would really love to see this, though, and I imagine many Finnish players would as well. I recall playing Mannikkala in Ostfront a couple of years ago, and a Finnish player on my team was really disappointed that the Axis side was comprised of stock RO Germans. No custom textures or anything to speak of.