Replicated Subsystems - Extensible GameState via subsystems rather than GameState Components. To setup please enable the plugin and reparent your GameState to AExtensibleGameStateBase, then just create a UGameStateSubsystem and it will be replicated and initialized automatically.
You can find an example of the functionality in UExampleGameStateSubsystem, it's disabled by default, to turn it on just change CreateExampleSubsystem = true in ShouldCreateSubsystem.
Hope you find a good usage for them in your projects <3
Because World Subsystems have bizarre and awkward lifetimes that highly complicate replication and networking. It is completely possible with Iris, but in practice it was actually very awkward to use and it didn't really offer many considerable benefits over GameState Subsystems other than a few niche usages.
The other more technical reason is because a subsystem is a singleton, by it's nature the patterns end up matching that of the GameState when it's replicated anyway - you can't really meaningfully implement a Subsystem that behaves like the Player Controller because the Server would require an authoritative version for each player with individual remotes having their local proxy of said subsystem. However that doesn't work because it breaks the singleton pattern on the server due to requiring multiple instances.
I am not the biggest fan of the Lyra Experience system, however I do see it's value - especially in GameState Components. However for some cases I think that it would be nice if they sort of just registered themselves and just worked, rather than needing to be manually added as a default subobject or added dynamically like Lyra Experience does. So I made this Subsystem type, and I find this solution to be a bit of a best of both worlds.
It can make it more straightforward to add code in auxiliary modules that require a GameState or replication without having to do any extra work other than reparenting the top-level GameState class. You can achieve the same with GameState Components with the right setup of course, especially if you're using Lyra, but it can be relatively easy to do it with these Subsystems.
It is still prone to the same limitations as the GameState and GameState Components - These subsystems do not exist on clients until the GameState has replicated. Therefore if you are looking for a solution that is immediately available on clients upon a World being created, this Subsystem type doesn't offer that.
When you want logic that can be dynamically added or removed based on specific GameStates you are probably better off just using a GameState Component for that as it's much better suited and designed for that purpose.
This code was designed to work on a version > 5.3 but it's likely possible to backport the code. It doesn't necessarily do any black magic or special things that are new to the engine. If something is broken, you can ping me at my discord handle "snaps" and i'l try push a fix asap.
Big thanks to Vori for helping me battle test it. PRs are welcome! Feel free to contibute <3