Only Romulans from the Northern Province have strong V-shaped brow-ridges.

Only Klingons from the Northern Province have a claw coming out of the top of their feet.

Only Trill symbionts from the Northern Province can blend with humans and take over their body entirely.

Only Trill humanoids from the Northern Province have strong V-shaped brow-ridges and no spots.

Only Cardassians from the Northern Province grow moustaches.

Only Vorta from the Northern Province can do the energy-ball thing.

I seem to remember Jeff explaining his choice, and a big factor was that Nebula doesn’t have comments under videos, nor any other similar forums for video posters and watchers to chat. I think he said he wouldn’t be happy without that direct interaction.