tbh, it would actually be interesting to see, whether in real life or at least a sci-fi type theory. Here's some thoughts I have on this:
There's the recent laws in the EU, the China firewall/botnet, the constant fears of cyber warfare, and so on. These sorts of things definitely seem like they could lead to such subnet splits. Laws in different nations or groupings of nations could become different enough to fracture them off from each other.
The question is: how will this split actually look? what groupings of countries will be involved in each? I imagine there could emerge a black market or some under-the-radar way to smuggle media from one subnet to another, assuming there is no legal way for people in different ones to communicate.
Let's assume that there is though. If there is in fact some legal yet highly limited, regulated, and probably very proprietary way to communicate across the nets, what would that look like?
Going back to CPU architectures and hardware, perhaps a long-term split may even lead to all countries settling on different stuff. Like instead of having everyone using x86 chips from Intel or AMD, and maybe ARM if they have a mobile device, perhaps each subnet will have its own standard. If not an actual standard, then certainly a de-facto one. Entire hardware platforms that could be region-specific. We've already seen Russia making their own CPUs, and I think China has been planning on doing the same sort of thing.
How deep could we go? would one of them eventually develop a new networking protocol beyond TCP/IP? Could it be that each net would be speaking completely different protocols at some point?
A lot of this hangs on the time frame here. How long would the net be fractured? If it's not for terribly long, then most of this stuff probably wouldn't happen, or would be at a reduced severity. However, if it ends up that such a split persists for, say, a decade or more, things start looking more probable.
This is actually getting kinda exciting, even as just an autistic theory. Shit, you could even make some kinda roleplaying scenario based on this