How are IL runs going to be submitted? Will all the level boards be re-updated for iceborne? Will people with iceborne installed just not be able to do LR/HR IL runs?

If you have the Iceborne expansion, you upload to the Iceborne Leaderboards This is for any mission, if you do LR/HR missions, you must upload it to this board.

If however you do not have the Iceborne expansion, you can still upload to the World Leaderboards

As of right now, if you're doing a run with someone who doesn't have the Iceborne expansion, it must still be uploaded to the Iceborne Leaderboards. Same if you do not have it, and someone in the party does.

Hope this clears some things up! Let me know if you have any other questions!