It's a bit of a shame that this project couldn't be rolled into Rockstar officially, or that another compromise could be reached. But as of today, the creators behind an alternate way to play GTA 5 online have announced they will be stopping development for good.
In a post on the GTA: Multiplayer website, the team writes that Take2 has asked them to stop production on the mod for supposedly infringing on the publisher's intellectual property. "Grand Theft Auto and all its content is produced by Rockstar Games Inc. and published and owned by Take2 Interactive Inc. We, as developers, respect other developer’s intellectual property and their legitimate interests."
"Rockstar’s developers have invested so much time to create this beautiful game. We have repeatedly stated our position: We are not going to cross this line, we won’t damage them. This was not an easy decision to make, because we have worked more than 2 years on GTA: Multiplayer. A lot of new friendships are created through it and we all have learned a lot during that time."
The post adds that the team had actually contacted Rockstar and received some feedback from them, but they noted that "Rockstar Games [is] only the developer" and Take2 has "to protect their own interests and those they have planned for [GTA Online] and further GTA games".
A video of the mod's latest test session was uploaded only last week, with a public version of the mod previously expected to be released in 2015. That's no longer happening, but it's interesting to see how far along the team had come.