I think that if they where to add on to the fountain/ base turrets I would like to see the beam be stronger, cause when I go Annie at level 18 I can tank a turret with Tibbers and 5 minions in less time then Tibbers and 3 minions dying (without the enemy team going after me) and get it either half way or more in few seconds since the new update. If I have a YI, Ashe, or a person with high attack speed we can get both the turrets down so fast.
I go as Annie and I can have Tibbers tank BOTH turrets while my team gets one entirely destroyed and as Tibbers dies we get the next with the tower focusing on one person who gets healed by the group. Or our super minions catch up and we wait for them to get targeted and then destroy the last tower.
I'd like to see the turrets have more resist to auto attacks. The idea of the shields and 3 laser is a really good idea. I 'd like to see those and maybe when the turrets take 3/5 damage they do twice as much damage to X (a minion, pet, player) from the laser, and from 4/5 they do more damage OR slowing effects so that they cant run from the enemy team from the fountain. Sort of like an AoE where the entire sight radius of the tower starts to slow or weaken all the champs and stuff in the range.
Like if the turrets did x2 or x3 more damage to summoned pets like Tibbers, Zyra's plants, or Voildlings etc, I think that would help the team being attacked re-spawn faster or do better against the enemy.