Lots of people are opining on this topic with requests varying in sophistication and complexity.
My request is simple. Provide a configurable maximum number of tabs to be kept loaded.
Tabs are then unloaded on a least recently used basis to maintain the maximum number.
The manual unload option, while better than nothing, is trivial and unsophisticated.
Asynchronous unloading will do. Dispense with 'weightings'. How hard can it be.