I would be great if you could add the statement from Optera, or a link to one in a forum somewhere granting permission. They have been extremely vocal, public and steadfast in their refusal to let this happen. A few quick searches in the usual locations don't really show a shift in this position. Something publicly available from Optera indicating they have changed opinions will go a long way to helping here.

However, I'll start working on porting LTN Combinator Modernized.

Will do. He did add me as a collaborator, so that is a clear indicator that he approved it. I did not just hijack the mod. ;-)

I only have a PM saying "If you want to tackle it, fine by me" and was added as a collaborator. I asked Optera to post a statement to the LTN forum.

Yeah, I considered the collaborator access as pretty solid proof / acknowledgement too. Not everyone may make the same, strong connection though.

Now, if someone re-uploaded a mod that violated the license, what would happen? Would the Factorio team delete the mod or what? Or would Optera go to court, demanding compensation? This whole licensing policy in the context of game mods is just a laugh, to be honest)

Now, if someone re-uploaded a mod that violated the license, what would happen?

Wube would obviously remove the mod and maybe remove the offenders ability to publish mods on Wube's platform.
Optera could sue, and given how anal some artists are about all this copyright / intellectual property stuff, that actually is a real risk if the offender is in a western bloc country actually giving a shit.

This whole licensing policy in the context of game mods is just a laugh, to be honest

Yes, it is a bit absurd given that they all not only stand on the shoulders of giants, but also on Factorio itself for their mod to make any sense.
In the end, if someone would want to copy the mod, the legally safe way to do it would be to look closely at the code and rewrite it, redo all art and publish under a different name with different texts. This is how the software industry does copyright evasion every day. You can't protect the idea of LTN, just the specific implementation.

Well, well. Here's an example of a mod that is clearly a copyright infringement: https://mods.factorio.com/mod/erm_zerg. And no one cares.

And no one cares.

If the copyright owner doesn't care, there, by the very definition of copyright, is no problem.
The linked mod's author mentions copyright information and their rationale for why they should be allowed to use it in the description.
Whether that rationale would hold in court or not in this specific case, I don't know. But to test that is the sole privilege of the actual copyright holder.

As usual, the most important law of civil law holds: If no one sues, there is no judgment.

I will lock this thread as off topic.