I would say for SB content there should be a ilvl check but only because stuff hits like a truck. Any ARR and even HW dungeons/trials, while it would be nice that somebody is up to parse with their gear, it isn't as crucial. Sure you might not finish the dungeon within 5 minutes but within 8, therefore I think personally it's whatever. Moment you step into siren song (or whatever that stupid dungeon is called) and you don't wear at least ilvl 260, you should remove yourself. Specially when playing tank/heals and trying to speed run it.
