That's mostly fine, but it complicates the scheduler and doesn't necessarily help performance. IIRC hyperthreading performs best when the workload on each thread is different (not taking caches into account), so running threads from the same process on the same core can (although isn't always; I'd hesitate to claim anything concrete here without benchmarks) be detrimental.

OpenBSD devs are likely open to it, but there are other inefficiencies in the kernel like locking that have priority.