The main purpose for a pink ward should not be the permanent vision aspect.
The fact that vision is impossible to acquire for laners unless they buy sightstone is ridiculous. As a top laner, I buy a Pink ward for the long term vision (because I dont have any other way to fucking get it) and it sucks that the enemy can just immediately take it out if they so choose.
I dont even give a damn if it had the ward seeing aspect on it, I needed the long term vision. For solo laners, the trinket wards do not last long enough and do not come back fast enough for them to be any decent vision really. Even by chaining them in the river theres still a time block that you dont have one, and theres another ganking method you havent warded as well.
The main objective of a pink ward should be to see other wards, not to use it as long term vision. Not only does the pink ward create problems with stealth junglers (because they can be destroyed instantly) theres just no decent way to get vision.
Green wards really need to come back.
having infinite duration not only makes it pretty useful, but gives it a certain flavor and makes it it's own item, on par with the advanced / legendary / mythic tier items, all of which have special characters and a unique function. Pink Wards: 1) Last indefinitely, 2) Grant True Sight, 3) Have a fair amount of HP and regen HP, 4) are visible and vulnerable. All these things serve to make thing Pink Ward an item in its own right, give it its own identity.