Droids are fun because of the idea of a good robot team, but they are not likely ever to be great again. The HK 88 86 Poggle Poe meta was early 2016 I think.
HK's leader ability is 50% tm on crit
Ok??? It's not that good of a leader ability when you compare it to new metas' abilities. Take Bastilla's protection and tenacity buff.
So then you're looking to good turn meter droid synergy to help it make sense. BB8 has the best imo. 7 or 8% turn meter for each droid ally at the start. That is something that matters enough to make the slower droids a bit competitive. My HK is g10 I think and only around 170 speed. To push his Meatbag Mayham to 210ish could be a game changer against a lot of opponents.
L3 would be a great tank to add. The newer players are all going to be getting L3, R2, and bb8 and maybe 88 as their droids so you are bound to see some combos of them here and there. What the 5th will be? Most likely T3M4. I don't see any reason new players would farm IG86 or HK at this point.
I think 88 and HK are the only droids with leader abilities. Then comes the most extreme idea: how about a droid team without a leader?
I think C3PO, chopper, L3, T3, and R2 might be a pain in the arse to fight. I wonder if it could be like a timeout team.