I have always wondered if a New GoI would pop up one day,and yes this was just a random Post.
Perhaps one could given it did something significant enough to catch the Foundation's attention. Usually a new GOI might be created if multiple articles have had incidents involving that one group.
A new GOI doesn't necessarily have to do something directly hostile(i.e attempt to unload missiles all over different sites), but it can be simple suspicion due to activities that may cause creations of anomalous objects/entities/sentient beings, or simply because they can possibly interfere in operations run by the Foundation, like the GOC, who often try to kill off anomalies with the claim of protecting the world.
This happens usually because another GOI may have a goal that contradicts that of the Foundation. The reasons are pretty much limitless.
It depends on if you mean in universe or out of universe, but the answer either way is yes, all the time.
In-universe, GOIs are any group related to the anomalous that the Foundation feels is worth monitoring, investigating, or documenting.
Out of universes, all that's necessary for a new GOI is for someone to write a successful article about them (although everyone is free to ignore that canon.) I believe Anderson Robotics is relatively recent, for example, and has a series of successful tales and SCPs about it.
If you mean something that is reaching the level of ubiquity of the big ones (GOC, CI, the Serpents Hand, etc.), that is also happening regularly too. There's a lot of work going into Maxwellism (a broken God offshoot), and Sarkicism in particular is exploding all over the place. Both in and out of universe, Sarkicism is rapidly emerging as a major power.
I don't know if things like that are edited into the GOI page, but it's happening all the time.