You can download The Frontier from Nexus Mods again now, and project lead 'Tgspy' has given an update on the situation in the now-closed comments section: Some contributors have also requested their music and voice lines be removed from the mod too, because they no longer want to be associated with the project. Players also criticised innapropriate content in the mod itself, and the devs have now made it availble again with some of the dodgier parts removed.
Last week, the creators of the huge Fallout New: Vegas mod The Frontier made it unavailable to download after discovering one developer allegedly posted 'animated pedophillic content' on their personal art accounts.