This is nothing more than curiosity on my part. Have there been any talk about connecting outposts on the frontier via subways? I already know the argument against it: Why? You can already teleport between the 9 outposts. My idea is a subway connecting the outposts with way stations every 500 or 1000 blocks. I imagine it like a web with the center outpost, in, well, the center. Each way station would also be connected to other way stations on the other main subway lines, just like a spider web. What's the benefit? Somebody that is between outposts could grab a train at a subway station faster than trying to walk to an outpost.
the 4 corner outposts are millions of blocks out, connecting them with rails (even through the nether) isn't really feasible. for the other 5 i don't really see a reason to connect them. you can pick up an elytra and several stacks of fireworks for less than 10k, and the distance between the player and the closest outpost will only ever be a few thousand blocks. with the railway you'd have to make your way to one of the stations, hope there is a minecart/boat there, then sit on a rail (or ice track) for a while to get back. with an elytra you can just fly straight back from wherever you are, in less time. build the rail if you so wish, it is my opinion however, that it would be a waste of time and resources.
I somewhat agree with you. That's why it's a curiosity question. OTOH, not everyone can afford elytras, especially the newbies.
I think the major issues with this are: 1) you'd plow through a lot of people's previous builds, especially within 1000-2000 blocks of each outpost 2) you might as well walk/run in the nether to get anywhere faster than an overworld minecart Both you could possibly somewhat get around by utilizing nether tunnels, but I don't see much use since most folks simply build their own nether highways. A nether highway system, even without minecarts, would be quite nice though, but I would see more use in them expanding outwards away from other outposts towards the world borders. Now, that would be quite the infrastructure project.
I had thought of a nether subway. There's already sort of one on SMP3 frontier east, but those are for specific places such as farms.
New players have or can get horses easily. Ice boats are faster than rails. Just making a 3 tall solid tunnel between areas would do for subway system. Lights installed to prevent mobs and alternate blocks with packed ice and a slab for the floor. Start with the destinations with most traffic and you might even get some help. It will still be a lot of work.