The peoblem is funding as allways. Both of them are similar and both of them are very expensive. Especially if you look at the USA, what I'm guessing this post if referencing. Your network is so unbelievably bad it takes a lot of muny to build up anything.
And even if you had intercity routes, you still need public transit in those cities to get there. Otherwise people have to drive there by car and if there already in the car they can just drive the whole way. And you would need huge parking spaces.
Parking spaces (especially in the USA) are a big problem. The point of a train station is to be in the middle of the city. So directly between shops and stuff like that. Huge ass parking spaces don't allow that, because you first have to walk some time to get to some "civilization"
(Yea sorry for the rant. Just can't believe how fucked up the USA is regarding car dependency)
The good thing is that building one helps build the other. One of the best ways to manage transit projects to build small, forward-thinking improvements that can contribute to a larger, patchwork network.
For example, reopening the Lackawanna Cut would enable new high speed sections of track between NYC and Pennsylvania/WNY/Canada. Future rail projects could then build new high speed sections around Pennsylvania/NJ or Toronto that would then cut transit times on both the Lackawanna Cut and the Northeast Corridor and/or The Canadian Corridor. Bit by bit, with just a few billion dollars at a time (instead of trillion dollar megaprojects), the American East Coast could become a world leader in intercity rail, on par with Japan.
The trick is to just get started improving existing rail corridors. It's not flashy and won't get you a million votes, bit it's the most effective way to do it.
This aggravates the hell out of me. Having one would generate a ridiculously large amount of cash. We have enough space on this continent for it to be the longest one in the world. Every one would flock to ride it as a tourist destination, never mind that it would draw of having the ability to see several major cities in one vacation. I could see it paying for its self in less than a decade.