I just hit 120 on my hunter trinity last week. I went into my first normal dungeon....and ilvl 400 items started dropping.

Apparently the following applies:
Normal Dungeons: 400
Heroic Dungeons: 415
Mythic Dungeons: 430

If you wanted to come back and try retail boxing and experience BfA dungeon content as a multiboxer, now's likely your best opportunity.