A glass-type item, which appears as a world portal the size of the glass in-game. This would be separate from other world portal items, like the Surface Division Field and the original world portal doors. In order to function, two world portals of the same size would need to be connected. The two items would accept inputs separately; the portal would only open when both items were fully activated. It would also be possible to use Start Reversed to flip the orientation of the portal, so they would face the inside of the voxel instead of the outside. This would ignore walls splitting up the glass, and generate the portal there anyway. Barrier Type would possibly be needed to prevent crashes, but would not change anything. The editor model would show the normal glass base along with two arrows pointing in/out of the portal, flipping to the other side when reversed.

In regards to the 4+ portals issue, I've found that setting r_portal_fastpath to 0 stops the bug. That being said, having lots of portals visible still degrades performance, so we'll want to have warnings about that.

Original screenshots, slightly outdated:

Reversing the portal would indeed change the editor model, something which was believed to be impossible at the time this issue was originally opened. The portal would also default to facing outward, instead of inward.

Connections to world portals would work differently, as described above.

As stated in the image, the logic gates seen here are simply used for demonstration purposes and would not be a part of the actual editor model.