I think it would be useful if you has better overview of nearby allies even if you are not in party with them:
If you are ungrouped, you could switch party interface to show n closest allies with ability to show only players or players as well as npcs.
Why? To show their health levels, conditions and boons and possibly other info (heart status as for normal party members) – this would be useful for coordination.
Also, some abilities affect only 5 closest allies, so it would be nice to see who exactly will they affect.
Performace: Client alrealdy knows this, so no extra data will be sent (it shows health and condition/boon related animations)