I live here and this railway thing has been coming up over and over again. Not to mention big-ass bridges across the sea and car tunnels. So let's see..
Although - they sell tickets from december 2018 as said on first post. First express should leave station approximately 24.12.2024
There are 3 different tickets available. €50 single, €100 return trip and €1000 one year unlimited. This is quite cheap because after this pre-sale, a hell breaks lose. For example, €2499 for whole year would be established. Buy yours HERE
Tickets are available for supporting the construction (that is still on paper literally) and prevent errors when the whole thing should start its duty.
I really like the idea though. ~30min ride to Helsinki, sounds nice BUT if there's a 30min security check too... Security is very important, but people would not agree with this amount of time. So again, let's see.