@darkfrei I've managed to get a minimal working version for 2.0. It's on GitHub.
Since my holiday officially ends next week, I might not work on it anymore for a while, and so I've invited you as collaborator to the repository. Anyone is of course free, and encouraged, to submit pull requests and open issues.
The mod works for base 2.0, but the graphics are bugged, I think this is because Factorio 2.0 regards all graphics as HR. I haven't updated the definitions for any prototypes that are not used in base 2.0.
Also, there is way too much duplicate code in the mod; I think it should be possible to make it procedural so that it generates linked belts for any tier that has undergrounds, just copy the graphics that are already defined, and change the tint slightly.