For the kinds of systems that are built with Erlang, which is a niche that Pony seems to want to occupy, I would argue it's inherently better to have preemptive

For the kinds of systems that are built with Erlang, which is a niche that Pony seems to want to occupy, I would argue it's inherently better to have preemptive scheduling. A cooperative scheduler will always be an open invitation for bugs relating to CPU hogging. Not having to worry about these things is priceless.