I had a situation a few days ago. Went in to Doma Castle as AST, I was geared up on Omega stuff so no issues on my end, and the DPS although one was new they both had decent gear. The PLD however came in with Augment Shire gear on the left side and a mix of 250-260 on the right. From the moment of the first pull the tank was squishy as hell and I literally had to spend every turn popping heals. They did a couple of big pulls and on each occasion we eventually wiped because the tank was so undergeared and taking bigger hits that could of been avoided.

Eventually i asked them why they were still using shire stuff and they just said they were being lezy leveling up. It kinda annoyed me more because this player was a Mentor, ok that doesn't mean much on most players but you'd think they would have some common sense when it comes to gear. After the 4 wipe the tank says it wasn't their fault and left the duty, we got a lovely (savage geared) replacement and we then had no problems from there on.

Having an ilvl requirement would be nice for some dungeons but it's more personal preference than anything. I'd try to gear up over time so I'd expect others to do it too.