Problem/Justification
(What is the problem you are trying to solve with this feature/improvement or why should it be considered?)
The problem I see is where you have a number of apps that use a lot of resources occasionally, but you still want to prioritize them when they do overlap.
Impact
(How is this feature going to impact all TrueNAS users? What are the benefits and advantages? Are there disadvantages?)
I can’t really see a disadvantage here, you just make the nice value default to zero and add it as another option in the “Resources Configuration” section. Perhaps with a little help icon to explain what a unix nice value is. People who don’t need it can just ignore it.
User Story
(Please give a short description on how you envision some user taking advantage of this feature, what are the steps a user will follow to accomplish it)
For example I have both jellyfin and immich installed. They can both use a lot of resources, and I want them to do their thing in a reasonable time. That’s usually fine because they are rarely active at the same time, but when they are I want to be able to prioritize jellyfin so whatever being watched doesn’t buffer. However simply limiting immichs resources would be a waste of compute the other 98% of the time.