> Does this mean that basically nobody is currently using OpenBSD in the datacentre or anywhere that might be expecting to handle 10G or higher per port, or is it just filtering that's an issue?

This looks like it only affects bandwidth limiting. I suspect it's pretty niche to use OpenBSD as a traffic shaper at 10G+, and if you did, I'd imagine most of the queue limits would tend toward significantly less than 4G.