Drones have always been an obvious problem. Whenever people talk about breaking Tau lists raising activations using drones has always been used. Hell the first Tau list iteration did it the first time the WPS played Epic at the CC (and won).
I'd like to add to your list another point - Tigersharks. In the background they carry 14 drones (3 units in epic terms). A formation of two could naturally carry a formation a 6. A vote for 6 strong formations?
A further issue is heavy drones - what's happening with ML's and what's happening with these. Should they be amalgamated into the same unit and it contain stats from both?
Another consideration is the special rules that affect drones.
You have expendable (which I think is universally agreed to be not applicable to all expendable formations).
You have the 'garrison' rule, that is drones allow the unit they are with to still garrison if otherwise able to.
And finally the jetpack rule which allows drones to either ensure their demise doesn't blastmarker too many allies or that cc reliant troops like terminators can ever touch them (did you realise these chaps can manoeuvre 20cm in response to an attack? Hell they could shift round so much that they could use enemy warengines to block los and all sorts

).
And finally the design consideration that drones are built into unit stats already. Should then drones be separate at all? Or perhaps heavily limited? (Say each formation of Tigersharks comes with a drone formation already loaded, or an air assault formation of firewarriors have drones with them as separate units.)
I do feel the 50 point bracket should be stuffed with drones

That is every formation gets the chance to add drones for 50 points. Of course how many drones and what they can do depends on the above!
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