Oblivious software person here: what does this new architecture mean for folks writing software on top of it? Is this a way to gain extra performance in single-threaded applications? What happens to concurrency? What's the long-term vision?
IIRC L4 is just a proof-of-concept thing to port, not necessarily what they plan for everyone to use. The Mill's security model is well-suited for a microkernel (it doesn't have the overhead traditional architectures have with microkernels).
The security model is probably the biggest thing people writing software will notice- instead of a user/kernel split with expensive transitions between separate address spaces, it's a single address space with cheap (on the order of a shared library call) transitions between arbitrary protection domains (turfs).
