I'd argue that the Utility Belt talent is the worst talent written for EotE Beta, since as it's written, that sucker is absolutely useless.
As for Knockdown itself, I do agree the abilitiy to trip someone up or put them on the ground prone would be nice, but it could also be overpowering, particularly if a successful hit isn't needed. The Disarm option can and has run into that problem, with a PC or NPC having missed their target by a country mile still causing that target to drop their blaster. And for a melee fighter, having a prone opponent in front of them makes it a very tempting option for PCs to render a tough foe Prone via Advantage, thus setting that foe up for the vibro-ax swinging Wookiee (or similar character type) to hew them into bloody bits of still-quivering sushi. In fact, might make it too tempting, particularly if there's more than one melee-capable PC and it's going to be several PC slots before the bad guy gets a chance to act.
I think unarmed combat really was intended to be very generic, and that such things as "pushing your foe to the ground" or "engaging them in a painful hold" was meant to fall under the purview of "the target suffers Strain damage instead of Wounds." Not very satisfying mind you, but there in the form of a blanket statement.
One of the biggest issues with the d20 versions of Star Wars was grappling. OCR/RCR, ultimately being a D&D 3.X clone, suffered from the overly complicated grappling rules. Saga Edition attempted to nerf this by making grappling the purview of characters that had takens specific feats, with additional feats making certain types of grapples a hell of a lot more effective (Pin + Crush + Bone Crusher + Rancor Crush = target taking damage and getting moved at least two steps down the condition track each round).
So at least for their Beta, the designers/developers opted to adhere to the KISS principle when it came to grappling and it's associated effects. Maybe we'll seet unarmed combat and grappling get fleshed out, though my guess would be such a thing would be a supplement rather than in the core rules.