We already have a europe-wide ticket. That would be the Interrail pass. Unfortunately it’s not intended for commuting and so it isn’t truly unlimited in one’s country of residence. Also costs a lot more than €49/month for unlimited travel, but includes high speed trains too (sometimes with a mandatory reservation charge)
I’d like to see a direct connection Schiphol-Frankfurt. There is already a direct connection Schiphol-Paris, there should be air-rail tickets sold on this route just like there are Brussels-Schiphol