Amusingly I actually have Video of Atari's Lead of Marketing playing OpenRCT2 on Stream, giving away RCT2 Keys to promote RCT World. To this day, Atari has left us alone though, so yeah it's pretty much not worth it to them to try anything.
Is there any way for a company, Lego in this case, to adopt a fan mod or remake, to make it legitimate IP/copyright wise?
Once fan projects get too much traction, companies have to cease and desist them because that's the way intellectual properties work in the law. It usually has nothing to do with whether it was a cool project or not, it's just that there's way too much money at stake when not defending your IP.