Towers do NOT need better scaling damage
Many people around the boards have been arguing that towers should deal greater ramping damage or even %HP True damage. If towers where to be given a change, however, it would be far better to change them in a completely different manner.
First of all, tanks survive towers fairly well. After all, it's their job to take as much damage as possible and, if they ever expect to successfully tower dive, they're going to require more time to do it since they deal far less damage and are usually more avoidable.
On the other hand, skirmishers and assassins revolve around skill. If a slayer dives a tower, their proficiency with the champion and the game versus the enemy should be the main determining points for the outcome of the dive. If they are tactful and precise, they should escape rather healthy with the target eliminated, if they are sloppy, they will most likely die without killing their target.
Now, a large problem arises when aforementioned slayers can practically waltz under the turret to destroy their target and leave relatively unscathed despite having eaten a volley of tower fire. It's far too easy for them to tower dive and effectively avoid the best insurance against them, placing yet another balance issue on the table.
Causing towers to deal more scaling damage effectively puts tanks out of the equation while hardly brushing assassins since tanks are going to feel the changes much worse than the assassins are (let's not forget health has been nerfed on most tank items, and while the armor buffs could compensate, turrets have a lot of armor penetration) due to how many hits they each take for a tower dive.
There are quite a few ways to address this issue in a different way, increasing the damage of the first few shots, applying a bleed effect, reducing armor penetration while increasing damage, etc. And while they vary in how good they are, most are clearly better than increasing the scaling damage of tower shots.
TL;DR Increasing the power of scaling tower shots won't hurt slayers much since they're out faster.