Healing turrets is a terrible concept because they will be unable to keep the healing up when the team is moving, and to compensate for that with more healing, it may be too strong sustaining bunker-style comps. Maybe if they make her gameplay pylon-based in some way that provides healing through an area, it may work. But it may also be too risky, and people may still simply move out of range and make your pylon base a waste of resources.
IMO, Support Sym 4.0 should move the TP back into her ult, and use the new open ability button to provide Photon Shields again, but improved both to fit the current power creep.
TP as an ultimate should be changed to be more active instead of a quick respawn mechanic. So, now when you press Q to place the teleporter, Symmetra stands in place while you control an aiming reticle that looks like Doomfist’s Meteor Strike, and can be moved freely around a certain radius from where Symmetra is standing. Once you decide the target area, TP exit is placed there, and TP entrance is placed where Symmetra is. It lasts only a short time, but can be used to go in and out. No line of sight required.
Photon Shields should work like OG Brigitte Repair pack (sudden burst of 150 shields, 75 overheal max, 4s cooldown), and make the shields deplete over time like an individual mini Sound Barrier. Make the decay heal the target for half the value they are decaying, so that you can also use it to top off allies between fights.
It would be an invaluable perk for the team if they also decide to make Shields the anti-burst mechanic (against Armor being the anti-chip mechanic), like I explain in this post. Being able to turn one ally immune to instakills would open a lot of possibilities against sniper strats.