==TL;DR:
scaling in it's current form isn't very fun. being able to turn it off for now would be appreciated.
==Long-winded opinion:
i've played both retail and Ascension at times when level scaling existed and when it didn't. IMO level scaling is a step backwards in terms of immersion and enjoyment.
without scaling, your character improves, becomes stronger, and moves to a different zone in order to find more challenging things to do. when you reach higher levels, it can be fun to return to "the old stomping grounds" and see how much easier it is to explore or farm crafting materials.
you get to see the difference very clearly between your old self and your new self. mobs that once rushed you and kept you from mining or gathering herbs, now barely glance in your direction, even when you stand next to them.
but with scaling, your character never outclasses or outguns the local mobs. if the boars in Ellwyn Forest scale with me all the way to level 100, why should i ever leave Ellwyn? why don't i just grind all the way to max level killing kobolds and spiders?
even worse: while the mobs scale in starter zones, they don't scale just 1 zone over. by the time you complete all the quests in Durotar, you're over level 20, and get sent to the Barrens. where mobs are now all grey because they didn't level up like the ones you fought doing the lowbie quests.
and the scaling seems flawed as well. it feels to me as though the mobs gain item level faster than the players. gear drops are less likely to be upgrades as you level up, and even items with higher ilvl seem more likely to be at best a sidegrade rather than an actual improvement.
the current form of scaling makes leveling new characters (or prestiging an old character) far less fun than if scaling were removed.
however, the idea of scaling being available, but not required, sounds like a great idea. if things like gear, quest rewards, character power levels, etc. could improve alongside the increase in power of the scaling mobs, it might be more fun. but until then, being able to turn it off would be a huge help.