1. Batching syscalls (and to me that implies copy-exactly-once IO, AKA Zero Copy in Linux/rust) means you can better manage the cost of performing syscalls and IO in high throughput and low latency use case. Eg if you expect a bunch of network packets, the physical card, driver, network stack should split packet headers and data in distinct buffers, each contiguous, in memory. With batched syscalls, you could also instruct the kernel to memmap a file in memory, and finally combine both syscalls into a single copy from Io to Io giving the memmap buffer as the output buffer to the network stack. I don't know how this could be done today, even with iouring, but I expect this would significantly outperform existing solutions as there would be a single copy operation instead of at least 3.

2. Per origin, per program, and per identity security context I think is required to deal away with the current prerequisite of all web browsers that the underlying system be uncompromised. Basically a world where every js bundle gets executed with it's own user as its own process and having to explicitly request access to your data.

3. Combined with the above to limit the risk of compromised root accounts, if they are limited to causing DOS and data loss it's much less dangerous than a world where your entire life can be usurped by assholes with a 0day. This implies major changes in driver architectures of OS/kernels but I think it's entirely unreasonable not to make these changes. The world has changed since the 90s.