That is a fantastic idea. Would you be attempting to have this be a built-in feature with the current filter system, or would it be more of a "set up a filter that includes items your friends would want"?
As an idea, having the ability to set up a party-wide loot filter, that you could add in everyone's individual filters to (perhaps adding an icon in the item's label?) Could work to reduce "is this showing for me or buddy #3? I'm definitely no developer so I have no idea of the implications with that, or if it's just rehashing exactly what you said, but I'm really excited either way. Love what you guys are doing, love the interaction with the community.
Just to be clear, this is one of those "I bet I could do it one day" things. It's not on a roadmap or plan.
Each player has 2 things they set up:
Priority loot filter rules. This would be as simple as clicking a star beside the rules in the filter list.
You can add rules to your own filters that say "recolour party member priority items blurple".
Then if an item drops for you that a party member has prioritized, it shows up blurple and you know to pick it up and tell a party member.
Could get even crazier with it and have an auto whisper the person who it was for.
Tons of painful things to set up in here but I think it would smooth out the experience so much.