The shutdown came on Wednesday of this week, following discussions between the mod's creators, the World Travel modding team, and Rockstar Games. Unlike typical copyright takedowns, this removal appeared to stem from a mutual agreement between both parties.
As mod team member nkjellman explained on Discord, the decision came after "friendly" conversations with Rockstar, which implies all parties came to an amicable resolution. "Due to the unexpected attention our project received and after speaking with Rockstar Games, we have decided to take down the Liberty City Preservation Project," the team stated.
As expected, the timing and nature of the takedown has incited speculation within the GTA community. Some fans and observers, including game reviewer Synth Potato, suggest the removal might indicate official plans for Liberty City's return. Current theories range from potential collaboration between Rockstar and modders to the possibility of Liberty City appearing in future GTA 6 content.
Given previous leaks that insinuated Rockstar had plans to expand GTA 6 over time by adding new regions, the Liberty City theories have been gaining traction in the community. With GTA 6 already confirmed to be set in Vice City, some fans seem convinced that Liberty City could be part of future expansion plans, especially for the online component of GTA 6.
It's not such a stretch to make this assumption considering Rockstar has previously hired FiveM developers and showed its willingness to work with the modding community. In reality, though, the takedown could simply be related to copyright concerns regarding the mod's use of licensed music and other GTA IV assets.
An alternate explanation, which might possibly be more realistic, is that Rockstar Games may be planning or working on a remaster or re-release of GTA IV. Historically, the company going after fan made remasters or graphical updates to older games tended to preced a re-release or official remaster; the mods in these cases would directly compete with a commercial product.
At this point, only time will tell if we'll be revisiting Liberty City either in remastered glory or in extra content for GTA VI.