This is kind of a strange time to bring up this topic, but I had a thought about the Veil after listening to Solas describe the Fade being a state of nature. This may get a bit rambly since I haven't really organized my thoughts about this much.
The Veil is the barrier between Fade and reality. If the Fade used to be a state of nature, that means that the Veil is actually more like a window.
Ancient elves used to be able to dream or enter the Fade and shape it with their will. The Veil in those times might have been more like an open window that let non-spirit beings crawl through and get to a state of mind/nature to where they can interact more directly with spirits or the Fade itself. Spirits don't really do well in the real world, so they stay on their side of the window, but can go anyplace to see/talk to/vaguely influence people. Like...ghosts without a corporeal form.
Imagine June consulting a smithing spirit who happened to wander in his workshop. Mythal talking to Justice, but it having no direct influence over physical reality unless summoned safely. Summoning a spirit is as much protecting yourself from it, as protecting it from the influence of the real world. Spirits who crossed over into the real world would definitely have been at risk to morph into another aspect of the mortal psyche, so I can't imagine many of the non-hostile spirits would choose to enter the mortal realm just to physically interact with something or someone.
Less hostile spirits would be totally ok with not going through the Veil and just being ghost-like in order to talk to people. More hostile ones would probably try to take advantage of the open Veil-window if they found a way to break through. That could mean possessing someone, or finding particularly weak points where the Veil is old, "cracked" or broken.
At some point in history, the Veil became more barrier and less window. It "closed" and the only way to "open" it now is a.) to dream,
be a mage, or c.) physically break the window so that you have a visible tear that anyone in the real world can interact with.
What could have caused the Veil to become like this? Perhaps hostile spirits were overwhelming the less-hostile ones due to terrible corruption happening within the ancient elven culture, or the pantheon itself. Maybe cutting off contact with the Fade caused "the quickening" in the elven people at the same time terrible stuff was happening to the gods?