How is a change like this going to be implemented? E.g. are they going to mainly update some tracks everywhere (and have two systems running in parallel), or all tracks in selected areas (and have passengers change), or something else?
Was there a comparable large scale rail infrastructure change in some other country?
Here's a helpful overview from wikipedia: https://de.m.wikipedia.org/wiki/Datei:Finnish_railroad_netwo...
I'm not sure how complete & up to date that is. But up north where the borders with Sweden and Norway are there isn't a whole lot of rail it seems. Norway's rail network doesn't extend that far. But Sweden gets pretty close to the Finnish border. I'm guessing a priority would be first connecting to their rail networks and then providing progressively more access to industrial hubs and eventually regional hubs.
This might also help with freight to the rest of Europe. Currently the only way into the country for freight is by ship (ferries, containers) or by road via northern Sweden. Sweden has decent north south rail connections and a bridge to Denmark. So extending coastal rail to Oulu would allow access to the rest of Finland for freight trains.
Just some thoughts.
There are a lot of options and I expect those planning this to look into all the details to figure out what they can do.
