Symmetra would not quite fit into current meta without some minor changes. I don’t think Ana is replacable and she with Lucio still have that synenergy with healing and Lucio’s speed boost is irreplaceable on KotH. But with Symmetra on team, all the tanks after one ulti would become even more deadlier and harder to kill than they are now and all the squishies would now not die from one roadhog’s hook combo. However she still won’t have the firepower of soldier at long range and her energy blasts can be eaten by dva’s matrix, even if she could possibly beat dva in close range now. Without soldier triple tank would be extremely susceptible to Pharah counterplay, even moreso than it is now.
I would imagine she could possibly replace Lucio on defending point cap, since that’s where her greatest strenght still lies. She can set up turrets to protect flanks while tanks keep chokepoint impenetrable with just Ana alone, her being the best burst healer currently and could heal everyone from relatively safe position. Symmetra could easily set up barrier for roadhog and dva to engage enemy safely and grab some easy kills with the hook and cook em method. And once she gets her ultimate setuped, tanks would become near impenetrable, long as support is on point. She could also be a replacement for Dva if 3rd tank is not needed on defence and opt for more healing support, since her photon barrier might allow for some dive in gameplay if it’s needed.
I’m also thinking that she might have potential on a dive comp with dva and zarya in tow. Zarya can bubble dva as she dives in to grab some focus fire while symmetra barriers rest of the team’s advance as they run in to the point. And once they secure the payload, she can easily setup 6 turrets around the payload, so anyone who wants to contest the payload would essentially have to get microed.