As the title suggests, I think a champion based on the 'brood-mother' / 'hive-mind' archetype has significant thematic weight - enough to warrant a champion in the League.
Not something like DotA's Broodmother, as she's a spider and we already have Elise, but an actual 'hive-mind' 'brood-mother' 'insect swarm' 'writhing mass' style champion. I imagine such a champion would offer a pretty unique silhouette while keeping with the purple-pinkish color scheme of the Void. Why the Void? I can think of no better vehicle for conveying the flavor of such a champion. Ideally, and perhaps uniquely, she would be the mother of her children while simultaneously being composed of them. Their collective physical forms and hive-mind would result in something greater than the two - her. (Don't ask me how it works.)
She would be reminiscent of Shub NIggurath, the Xenomorph Queen, the Flood, the Zerg, the Tyranids, the aliens from Slither, and even the hellions and the eldrazi from Magic. For an even more obscure, but recent, take on a similar idea, check out Apex from Android: Netrunner!
As far as her personality, I imagine she'd have a multi-layered, echoing voice (a sort of 'we are legion' thing), and, like most Void champions, would be hungry (she has to feed her babies after all, while also conquering new 'hunting grounds' for them), but haughty in a vicious alien sort of way. Lore-wise we could say she is one of 'some number' of Queens of the Void, and whereas Cho and Kog and the others are like the vanguard, she's there to 'colonize' Runeterra. You could even do an event where her arrival signifies a momentous moment in history - that of an existential crisis on the horizon. Think of the moment that Command Shephard in Mass Effect learned that the Reaper they had just killed was just the first. More, countless more, were on the way.
I would like to see her be a support (why would the Queen want to be on the front lines fighting doing the heavy lifting? better to sit back and dictate the flow of battle...) and perhaps play with vision or detection in some way. As far as her niche as a support, that would probably be up to her kit and its functionality. She could also seemingly function in the jungle just from a thematic perspective.
I would like to offer some key words that I think better communicate the intended flavor. I want you to think: swarm, hive, larva, drones, parasite, tentacle, seed, egg, hatch, synaptic, slither, collective, brood, implant, insect... I'm sure there's more!
My point is that it's an archetype, a fantasy, that we haven't seen in the League. Not only that but I'd be willing to bet such an idea would resonate with people as well as be identifiable across cultures. I'd love to see what Riot could do with it!
EDIT: Ability Sketch 1.0
NOTES: ~, the Brood Mother is composed of her children, the hellions. Her abilities and basic attacks revolve around using them. Her resource is her health (and subsequently her hellions.) There is no limit to the number of hellions that can be in her swarm. Her swarm, if sufficient in number, can pass over terrain. Her hellions will die off as they attack enemy champions.
P: Hellion Swarm: ~'s basic attacks do not utilize projectiles. Instead, she creates several hellions at the cost of a sliver of health. They move and attack as single unit (via Alt-Click), grant vision around them, and can be targeted and hit by attacks, spells, and abilities as though they were a champion unit. Subsequent basic attacks will add more hellions to the swarm.
Q: Parasitic Implant: ~ slings some of her constituent hellions in a direction. Upon colliding with an enemy champion, it impregnates them, dealing % current health damage each second for 7 seconds. At the end of that time, several hellions burst from them, dealing % maximum health damage.
W: Synaptic Node: ~ leaves some of her constituent hellions behind in a location, gaining sight of the area. (Also, they will visibly writhe / appear agitated when stealthed champions near them.) There the hellions gestate over the next minute, increasing in number. She can move over the node to add those hellions to herself, healing her. Alternatively, moving her swarm over the node will add the node's hellions to the swarm.
E: ~ disperses, scattering her constituent hellions everywhere, becoming untargetable for the next 5 seconds. Her constituent hellions will attempt to converge on her previous location, attempting to re-coalesce. They will latch on to, attack, and slow enemy champions they encounter during their path. She can activate her W during this time to cause her 'consciousness' to jump to the nearest node within range. Her hellions will attempt to converge on that node. She retains her ability to control her swarm during this time. Reactivating this ability will cause her to recombine on the spot, drawing in ALL hellions in a large radius (including her swarm.)
R: ~ does something cool. Still thinking on it.