"New Identity for this Site"
We have "New Circuit for this Site", but the cache and other supercookies for that first party are not wiped. Only the stream is changed.
It should be possible to implement "New Identity for this Site", for example by incrementing the container ID. (Note however that containers are not as strict as first-party isolation, so it might be better to introduce a new counting mechanism into origin attributes that shares the same strict policy as FPI.) In that case, all supercookies would be wiped and a fresh circuit used.
See also legacy/trac#28316 (moved).