They put a telegraph cable under the ocean in 1858. With all the technology (including materials) we have today, I bet it's very feasible from a technological point of view.

An economic point of view is a different question, though.

It's interesting to speculate on how it could be done. Maybe it could be soft, like a fire hose, and kept open by internal pressure. That way it could be unfurled from a ship. Rigid pipe seems pretty difficult.

Rigid steel pipe is the only feasible way, I believe. Current longest subsea pipeline (Nord Stream) is 760 miles.

Here's how it's done (it's pretty darned fascinating):

https://youtu.be/EyrdjqEiTZc

Yet there's the whole thing where the end points are on tectonic plates moving away from one another...

Okay, maybe a little flexible would be good!

Flexible pipe for subsea O&G has existed for a long time now (it's certainly not soft, but it is flexible and it is installed from huge spools):

http://www.technip.com/sites/default/files/technip/fields/pu...

O&G technology is pretty amazing. I guess you can develop some pretty amazing technology when you can invest many billions of dollars over many decades, because the payoff is huge. Makes you wonder where other technologies would be with that much expenditure.