My gut feeling though is accel-set would be more logical being done
first, as that also influences the set of features available in other
areas of QEMU configuration. Was there a reason you listed it after
machine-set ?
That was also my initial gut feeling, but actually right now the machine influences the accelerator more than the other way round. For example the initialization of the accelerator takes a machine so that for example on x86 the per-architecture KVM knows whether to set up SMM. Also different machines could use different modes for KVM (HV vs PR for ppc), and some machines may not be virtualizable at all so they require TCG.
The host CPU these days is really a virtualization-only synonym for -cpu max, which works for TCG as well. But you're right that x86 CPU flags are dictated by the accelerator rather than the machine, so specifying it in machine-set would be clumsy. On the other hand on ARM it's a bit of both: for KVM it's basically always -cpu host so the accelerator is important; but some machines may have an M profile CPU and some may have an A.
I don't have the sources at hand to check in which phase CPUs are created, but it's definitely after ACCEL_CREATED. Adding a third command cpu-model-set is probably the easiest way to proceed.
Paolo