It would be so easy to implement and would be something that could be a challenge depending on what the modifiers are. Lets be honest, most of the 315-320 players can do the raid in their sleep with a competent fireteam. Adding this might spice things up a bit and add another way people could get that last item they need to reach 320.
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not 310 to 320... rather 315-320... because that's what people need. We're all above 310 by now, well probably most of us...