Why is there a strong reason that we need a hard coded fade out limit at all?
If, like in your example, a user set up an echo with a feedback value of 1 he probably knows what he is doing and he want have an echo to entreaty. Any automatic decreasing of the feedback after a hard coded time, will limit the use cases and might be an unwanted behavior.
The user can always right click to cut an never ending the effect or the effect can disable itself.
Why is there a strong reason that we need a hard coded fade out limit at all?
If, like in your example, a user set up an echo with a feedback value of 1 he probably knows what he is doing and he want have an echo to entreaty. Any automatic decreasing of the feedback after a hard coded time, will limit the use cases and might be an unwanted behavior.
The user can always right click to cut an never ending the effect or the effect can disable itself.