The biggest bottlenecks are probably network latency, reliable synchronization between nodes, and keeping the system secure without adding too much overhead.
At testnet scale, the hard part isn’t just making quantum networking “work” in theory — it’s making it stable, measurable, and usable under real-world conditions. That means handling noise, managing performance trade-offs, and making sure the protocol still plays nicely with the rest of the stack, especially if hybrid signatures and Substrate components are involved.
In short: scalability, stability, and integration are probably the main hurdles.